Losing weight in england works the same as it does here
All kidding aside, walk as much as you can, maybe a friend can get you a pass to a gym while you're there.
Try and do grocery shopping and prepare your foods just as you would at home. As for food, I personally find it a bit more difficult to find heathfood stores, or the variety of organics and vegetarian fare I have in nyc, but you just have to look a bit harder. Waitrose is a pretty nice grocery store and London has a whole foods.
But don't pressure yourself. Nothing is going to magically happen in england to better your chances of weightloss.
If you focus on getting exercise in (biking on the coutryside is lovely) and eating right, you should be fine.