North America foreign license
The FAA issues a special license (must be applied for in advance) which can be used on the condition that the foreign license is current and that means also a current medical. It's a bit of bother because one also needs to be accepted on a CFI checkflight etc etc. It helps to know local airregs and notams etc etc.
If you fly a UK registered aircraft your UK license is accepted, but you must be familiar with local airregs etc. It is best to read the regulations before setting your hopes high.
Glider licenses are somewhat easier to get to fly in the states.
And don't forget that a private license does not allow taking passengers for compensation or the receipt of flight pay!