visas for usa
At a recent INS (immigration) meeting with FBI it was considered that the USA is "at war" so you should realise that security is the paramount concern. In fact there was a security notice issued today re-emphasising the security measures for GA traffic.
However it is possible to undertake genuine flight training on an M1 orJ1 visa. The catch is that these are issued for one year or two year periods respectively for genuine training only. Futher caveats to the J1 visa is that it wil only be issued to ab initio students or those with 50 hours or less with no greater than a ppl (but does give the opportunity to "work). You would be expected to stay for a reasonable period of the visa (say 3 months of the M1).
Other rcecent changes are that a FSDO can no longer issue
a FAA licence on the basis of a "foreign" licence without a lenghty 60 day validation process, which for the UK may be longer as the CAA have pointed out the large numbers of validations that they may have to process, on the other hand you can simply take the FAA written and flight test if you have the necessary flight hours. You should not turn up at immigration on your way into the USA on the visa waiver programme intending to do flight training, hours building or even just local flying as you will be turned straight back if your intentions are dicovered. Like most things it is not impossible to fly as you can still do a dicovery flight with a US instructor if you just want to look around from the air, though a reputable school may carry out some fairly thorough checks on you.