Names which are popular in
UK and not US:
Boys:
Alfie ArchieFreddieHarveyCallumOscar (not that unusual in US, but waaay more popular in
UK)
Toby (see
Oscar)
Arthur (see
Oscar)
FinlayRhysStanleyJenson (probably because of Jenson Button)
Girls:
MaisieMillieRosieEvieTillyFreyaIslaImogenMatildaMarthaHarrietFlorenceEsmeNiamh
I don't really have an idea of "British" names, because I'm British anyway, but there are some names which I think American would consider British (because they're posh or a bit quirky), such as:
Violet
TheodoreArchibaldCecilCorneliusQuentinCrispin
However, none of these are actually popular any more!