Bright kid :-)
There are groups that teach young kids to code, such as this one in the Netherlands: coderdojo-utrecht.nl
It says you're in London, which is like 25x bigger than Utrecht, perhaps there's something similar?
It seems to be pretty popular. That particular group has a minimum age of 7, but it's just an example. They use Scratch as well, that seems like a great place to start.
(I didn't find raspberries particularly easy, but that was pretty early on, hopefully they've become easier? My instincts would be to go with a cheap normal PC).