It can be so confusing distinguishing between UK, Great Britain, and England. So probably the best way to do this is by the yellowing of their teeth and how Dickensian their accents are. The teeth come in various shades of yellow.

Putrid yellow means their English and they’ll probably ask you for a penny farthing for supper with a cup of hot cholera, guvnor. Great British means their teeth will be the colour of warm piss with breath like cancer. If they’re from the UK their teeth are the colour of nicotine with hair like a cesspit. Or you could watch this video, which is probably more accurate.