The term 'British' is often used as an overarching term to refer to people originating from the United Kingdom as a whole, while 'English' specifically refers to those from England. It's not necessarily a matter of saying 'were' but recognizing the different geographical and cultural identities within the United Kingdom.
It is also worth noting that the use of these terms can vary depending on context, personal preferences, and regional differences within the United Kingdom. Some individuals may identify more strongly as English, Scottish, Welsh, or Northern Irish, and may prefer those specific terms to describe their identities.