Claire Foy was on 'The Tonight Show Starring Jimmy Fallon' and, sure enough, Fallon shoved the shiny mic into her hands. To be fair, she was able to do it beat-for-beat and even had the fast "Bubba to the bang bang boogie, boobie to the boogie / To the rhythm of the boogie the beat" down to a tee.
It seems to be a recurring theme with excessively British actors knowing rap staples. Daniel Radcliffe, for example, was able to recite Blackalicious' 'Alphabet Aerobatics' with incredible dexterity. They must teach at LAMDA or RADA or something.
Check it out.