spils: I reckon every new PPL should have a flying buddy (right
1013.5 
) - whether they learned in UK or US. It just makes so much sense to fly with someone else at a similar level as you can learn from each other (good stuff and mistakes!) and halve the workload in what might otherwise be difficult or daunting conditions in the early stages. A wonderful morale and confidence booster, and a great way to make friends. Besides, you'll find that friends and family don't find destinations that are "just another airfield" as interesting as your fellow fresh-PPL'er will!
Having learned and mostly flown in the UK, and only managed half a dozen hours in each of the USA and France/Spain, I would imagine the specific points you will find you need to adjust to will be:
- Weather - more changeable. Get an instructor to refresh you on precautionary landings, low-level circuits, and low-level nav.
- Airspace: more of it in the way at low levels, and some Class A all the way down to the surface (not just down to 18,000' as in the US! Not as daunting as it looks on the map, but I would imagine if unfamiliar it might be. These fears will soon be dispelled once you become accustomed to things around here, and will be where you get most benefit from teaming up with a UK-trained PPL.
- R/T - the differences are not immense, but may be a bit bewildering. Not just phraseology (i.e. we use QFE, yanks don't - nor do French and many others...), but also what units (e.g. LARS) are available, and what service you are likely to get.
- Circuit joining procedures: we don't do 45 degree d/w joins that are common in the US. Be familiar with what a so-called "standard" overhead join is here (get an instructor if need be), and then understand that its different at almost every airfield in the country But the basic system is still important to fully understand in practice (not just from a book), and I think make sense anyway.
I would recommend a useful exercise to do ASAP would be to pick three or four "local" airfields closest to your home airfield, within say 30~50NM, and then spend an afternoon flying to and landing at each. This will make you more comfortable and less hesitant in case you one day need to divert to one of these due to poor wx or some other reason on a return trip to home-base one day (it happens!).
Then set yourself (and your new found flying friend) some dual cross-country expedition exercises that can provide experience of a variety of problems. For instance, I'd recommend a day-trip aruond the London TMA, which would include some "squeezy bits" of airspace. E.g. from wherever you are (was it Popham?) to say Blackbushe, then Wycombe, then say Southend, then around to Biggin Hill, then back via Farnborough. Land at a few of these to make it more interesting, and to stock up on food/drink and empty bladders etc!
I'm sure you can imagine some variations on this theme. Once you've done two or thre exercises like this, I guarantee you'll feel more comfortable, and will be much more safe and familiar with the environment you're in. Again, I'd recommend this process to any new PPL.
Hope this is of use,
Andy