The starting point: https://www.bbcgoodfood.com/recipes/sourdough-bread
My adjustments in italics.
Method
- STEP 1
First, make your starter. In a large bowl, mix together 100g of the flour with 125ml slightly warm water. Whisk together until smooth and lump-free.
- STEP 2
Transfer the starter to a large jar (a 1-litre Kilner jar is good) or a plastic container. Leave the jar or container lid ajar for 1 hr or so in a warm place (around 25C is ideal), then seal and set aside for 24 hrs.
- STEP 3
For the next 6 days, you will need to ‘feed’ the starter. Each day, tip away half of the original starter, add an extra 100g of flour and 125ml slightly warm water, and stir well. Try to do this at the same time every day.
- STEP 4
After 3-4 days you should start to see bubbles appearing on the surface, and it will smell yeasty and a little acidic. This is a good indicator that the starter is working.
- STEP 5
On day 7, the starter should be quite bubbly and smell much sweeter. It is now ready to be used in baking.
Making Bread
The Starter is now known as the Mother. Take half the mother and add 100g of flour and 100ml of water, mix well and allow to work overnight. This is now known as the Levain.
- STEP 6
Tip 500g flour, 225ml warm water, 1 tsp salt, 3 1 tsp sugar and the starter into a bowl, or a mixer fitted with a dough hook. Add 225ml warm water, slowly. Stir with a wooden spoon, or on a slow setting in the machine, until combined – add extra flour if it’s too sticky or a little extra warm water if it’s too dry.
Forget the mixer, do it by hand. 17/11/23 Only used 1 tsp sugar. Apparently sugar gives you a harder crust. Today's loaf was as large as the last loaf, but with just 1 tsp. And I only used about 200ml of the water.
- STEP 7
Tip onto a lightly floured surface and knead for 10 mins until soft and elastic – you should be able to stretch it without it tearing. Ignore this: If you‘re using a mixer, turn up the speed a little and mix for 5 mins.
- STEP 8
Place the dough in a large, [well-oiled - No] floured bowl and cover. Leave in a warm place to rise for 3 hrs. You may not see much movement, but don’t be disheartened, as sourdough takes much longer to rise than a conventional yeasted bread.
- STEP 9
Line a medium-sized bowl with a clean tea towel and flour it really well or, if you have a proving basket, you can use this (see tips below). Ignore this.
Tip the dough back onto your work surface and knead briefly to knock out any air bubbles. Shape the dough into a smooth ball and dust it with flour.
- STEP 10
Place the dough, seam-side up, in the well-oiled bowl or proving basket, cover loosely and leave at room temperature until roughly doubled in size. The time it takes for your bread to rise will vary depending on the strength of your starter and the temperature in the room, anywhere from 4-8 hrs. The best indicators are your eyes, so don’t worry too much about timings here. You can also prove your bread overnight in the fridge. Remove it in the morning and let it continue rising for another hour or 2 at room temperature. The slower the rise, the deeper the flavour you will achieve.
- STEP 11
Place a large baking tray in the oven, and heat to 230C/210C fan/gas 8. Fill a small roasting tin with a little water and place this in the bottom of the oven to create steam. Remove the baking tray from the oven, sprinkle with flour, then carefully tip the risen dough onto the tray.
- STEP 12
Slash the top a few times with a sharp knife, if you like, then bake for 35-40 about 25 mins until golden brown. It will sound hollow when tapped on the bottom. Leave to cool on a wire rack for 20 mins before serving.
Looking after MotherKeep Mother in a slightly warm place. every other day pour off half and add about 100g of flour and 100ml of water, stir slightly and put away again. You can always use the 'discard' to make more bread!
CommentsI think that I have cracked it. In step 6, do not add all of the water at once. Mix up the flour/sugar/salt with the levain, and then add water until the mixture starts to stick together. While kneading it, add just enough water to make a ball that you can knead. Too much and it will be a runny mix later when you pour it into the baking pan and come out flat. 
22/11/23 A suggestion to keep it warm while rising was to put it in a slow cooker. I did this, occasionally turning it on to low for 5 minutes to warm it up, but I noticed that the temperature got too high. I think it over did it and when I poured it on to the baking tin it looked OK'ish but fell flat as it started cooking.
Links:https://thedoughacademy.com/7-reasons-your-sourdough-bread-is-collapsing-how-to-fix/
https://www.busbysbakery.com/sourdough-bread-not-rising/
https://www.mydailysourdoughbread.com/sourdough-not-rising/
https://bakesmartly.com/common-reasons-why-your-bread-isnt-rising/
Questions: Why do some recipes want you to add sugar/honey and others don't? Sugar doesn't do anything for the yeast but helps to get a hard crust. Why do some recipes go straight from the mother and not use a levain?
28/11/23 Today I used the suggestion 11 from the last reference above and added the water to the flour to 'autolyse' before adding the starter and salt and sugar. I also didn't knead it much but just folded it over a few times. When it went in the oven it spread out as it it was soggy, but it did rise a good bit. I shall have to consider how to adjust this.
7/12/23 Have started a loaf the same way that I did the last one. Totally different from the initial steps from the BBC recipe. Started Thursday evening about 7PM.
Measured 500g flour into a large bowl (100g Wholewheat, 400g white) and added 1tsp salt. Poured half the Mother into another large bowl. Warmed 225ml of water. Mixed up the flour and salt with my hands and added it slowly to the bowl with the starter, mixing with my hand. Added a bit of water. Put the solid mass on the table and started kneading and folding it, adding more of the flour from the bowl to it, and occasionally dripping some water on to it. Kept doing this until all the loose flour was part of the mass. I added a little bit more water and it started to get soggy so I kneaded it a bit more then put it into a bowl, covered it and put it into the airing cupboard overnight. I had about 50ml of water left. In the morning I kneaded and folded it a bit more, only about a minute, and then put it in a buttered corningware bowl to rise during the day. I then cooked it in this corning ware bowl, and this is the result. 
Unfortunately it did stick a bit to the bottom of the bowl. But I am pleased overall.
27 Dec 2023. A good loaf. 200g Wholewheat/300g White.Last night about 6, I split the mother, and refreshed both parts with 100g flour, 100ml water, and put the one that I was going to use in the airing cupboard for about 3 hours. Then I added the ingredients and kneaded it , and as I worked it I kept adding dribbles of water, and finally when I put it to rise overnight it was slightly moist around the outside. Funny enough this way I had less stuck to my fingers than usual. About 11 in the morning I folded it a few more times then put it in the oiled square corningware back in the airing cupboard. It rose well, but deflated when I scored it, and cooked it about 5 o'clock.
8 January 2024 A good loaf. Photo compares it to a breadmaker wholemeal loaf, which is taller but not so large around. This has been a 36 hour process. I split the mother Saturday evening as described above. Sunday Morning I made the loaf with 400g of mixed White and Wholemeal bread flour, and allowed it to rise in the airing cupboard. Sunday evening I reworked it, put it in the corning ware dish, warmed up the oven for a couple of minutes, and then left the bread in the oven overnight. Cooked it (gas 6 - 25 minutes) Monday morning and this is the result on the left. 
- STEP 1
First, make your starter. In a large bowl, mix together 100g of the flour with 125ml slightly warm water. Whisk together until smooth and lump-free.
- STEP 2
Transfer the starter to a large jar (a 1-litre Kilner jar is good) or a plastic container. Leave the jar or container lid ajar for 1 hr or so in a warm place (around 25C is ideal), then seal and set aside for 24 hrs.
- STEP 3
For the next 6 days, you will need to ‘feed’ the starter. Each day, tip away half of the original starter, add an extra 100g of flour and 125ml slightly warm water, and stir well. Try to do this at the same time every day.
- STEP 4
After 3-4 days you should start to see bubbles appearing on the surface, and it will smell yeasty and a little acidic. This is a good indicator that the starter is working.
- STEP 5
On day 7, the starter should be quite bubbly and smell much sweeter. It is now ready to be used in baking.
Making Bread
The Starter is now known as the Mother. Take half the mother and add 100g of flour and 100ml of water, mix well and allow to work overnight. This is now known as the Levain.
- STEP 6
Tip 500g flour, 225ml warm water, 1 tsp salt,
31 tsp sugar and the starter into a bowl, or a mixer fitted with a dough hook. Add 225ml warm water, slowly. Stir with a wooden spoon, or on a slow setting in the machine, until combined – add extra flour if it’s too sticky or a little extra warm water if it’s too dry. Forget the mixer, do it by hand. 17/11/23 Only used 1 tsp sugar. Apparently sugar gives you a harder crust. Today's loaf was as large as the last loaf, but with just 1 tsp. And I only used about 200ml of the water.
- STEP 7
Tip onto a lightly floured surface and knead for 10 mins until soft and elastic – you should be able to stretch it without it tearing. Ignore this: If you‘re using a mixer, turn up the speed a little and mix for 5 mins.
- STEP 8
Place the dough in a large, [well-oiled - No] floured bowl and cover. Leave in a warm place to rise for 3 hrs. You may not see much movement, but don’t be disheartened, as sourdough takes much longer to rise than a conventional yeasted bread.
- STEP 9
Line a medium-sized bowl with a clean tea towel and flour it really well or, if you have a proving basket, you can use this (see tips below). Ignore this.
Tip the dough back onto your work surface and knead briefly to knock out any air bubbles. Shape the dough into a smooth ball and dust it with flour.
- STEP 10
Place the dough, seam-side up, in the well-oiled bowl or proving basket, cover loosely and leave at room temperature until roughly doubled in size. The time it takes for your bread to rise will vary depending on the strength of your starter and the temperature in the room, anywhere from 4-8 hrs. The best indicators are your eyes, so don’t worry too much about timings here. You can also prove your bread overnight in the fridge. Remove it in the morning and let it continue rising for another hour or 2 at room temperature. The slower the rise, the deeper the flavour you will achieve.
- STEP 11
Place a large baking tray in the oven, and heat to 230C/210C fan/gas 8. Fill a small roasting tin with a little water and place this in the bottom of the oven to create steam. Remove the baking tray from the oven, sprinkle with flour, then carefully tip the risen dough onto the tray.
- STEP 12
Slash the top a few times with a sharp knife, if you like, then bake for 35-40 about 25 mins until golden brown. It will sound hollow when tapped on the bottom. Leave to cool on a wire rack for 20 mins before serving.
22/11/23 A suggestion to keep it warm while rising was to put it in a slow cooker. I did this, occasionally turning it on to low for 5 minutes to warm it up, but I noticed that the temperature got too high. I think it over did it and when I poured it on to the baking tin it looked OK'ish but fell flat as it started cooking.
https://www.busbysbakery.com/sourdough-bread-not-rising/
https://www.mydailysourdoughbread.com/sourdough-not-rising/
https://bakesmartly.com/common-reasons-why-your-bread-isnt-rising/
Unfortunately it did stick a bit to the bottom of the bowl. But I am pleased overall.
