To follow on from what Genghis said...
If you're not going to be able to afford much flying after getting your PPL, then learn here - unless your aim is simply to get the PPL, then stop. Why? It'll give you a longer period of flying, hanging around flying clubs, being involved in aviation. In that time, you can find people to fly with after you've got your licence, find out about cheaper ways of flying, get information generally. You'll also hopefully build up sympathetic school and instructor contacts, which will be helpful if you're going to be needing lots of check flights after you've passed, or lots of advice anyway. And having learned over a longer period, your skills will degrade more slowly, ie you'll get rusty less quickly!
I should imagine that learning in 4 weeks, coming back to the UK and doing a few hours, then trying to fly with not much in the way of money, experience, or contacts over here, would be pure hell. No wonder so many people who try it give up!