I will point you in the right direction within this site, from the things you can do holding a Foundation Licence where there will be a dedicated page coming soon for the Foundation Licence
The RSGB is Britain’s National Radio Society, the proof is in the name “Radio Society of Great Britain” check out their website at rsgb.org.They have a monthly magazine called Radcom which (I think) is a great read with news, views and different articles from all around the country. Their website is there to lend a guiding hand should you need it. They can arrange exams there and point you in the right direction.
HF is definately the place to be with a Foundation Licence, I remember my first ever HF Contact, speaking with LZ177GL in Bulgaria on 5 Watts, yes that’s correct just 5 Watts 14 MHz on a Yaesu FT450 that my daughter bought for me and don’t forget as a Foundation Licence holder you now get 25 Watts.