Interesting as I seem to recall a decline over the previous decade.

My guess is that events have strengthened the British identity in terms of making it more prominent. First you had the Scottish referendum in 2014 which had the nationalists failing and Unionists/middle voters being re-enforced in their British identity. Then you had the EU referendum and Brexit, which also would have had the same effect. Then we've had other events like royal births and the Diamond and Platinum Jubilees which again help to reinforce national identity - I would expect if you retook the census in a years time, the death of QEII and coming Coronation of KCIII will also serve in the same manner.

Personally I tend to identity as British for my nationality, but English when it comes to ethnic background/race.

How about you?