Learning to fly

40 years or so ago, I learned to fly, at least a bit. I did some solo
circuits in gliders. I would like to come back to flying, and I was
wondering about whether to learn on powered or unpowered planes?

If I learn on gliders, will this be any help towards getting a PPL? I
apprecaite that it's all good experience, but I have a feeling that the PPL
only counts hours in a powered plane. Is that right?

Also, any recommendations for places to learn to fly, powered or unpowered,
near North London?

Finally, I am very overweight (over 18 stone). Does that rule out gliders
unless I lose quite a bit of weight?

Thanks very much.