Learning to fly in the US is the best move I ever made. GA is great over there, and its not a rip off. I rented a year 2000 Archer 3 yesterday, complete with 2 axis autopilot and IFR approved GPS, and the cost....about 60 GBP per hour wet. Beats the crappy old dogs I rent at home for 100GBP per hour.
When people tell you that the weather is 'perfect' in the states, and you won't learn to handle real weather, then don't believe them. Try flying through the Banning Pass on a hot day on your way to Palm Springs, then you'll experience real turbulence !
I seriously recommend learning in the US, especially California. Here you can experience so much that you'd never experience in the UK, for example high altitude airports, flying over REAL mountains (not the hills we have in the UK!)....Also if you go to some of the schools at Long Beach, you can get your RT exam while you're in the states, so nothing extra to do when you get home.
Don't be worried about the RT / differences in flying between the US and UK. I was lead to believe that 'it was so different'....Not true, if you learn at Long Beach, or somewhere in the LA Basin you can handle anything in the UK, probably including LHR....I'd say its more the other way round, people who learn in the UK cannot handle flying in a busy environment like LA.....
All the best....