This is a discussion for another thread, perhaps, but from 2010 onwards this has been happening, so it's not something just fuelled by Brexit.
Traditionally Labour constituencies that have been Conservative held for some time include Blackpool, Bolton, Mansfield: they were added by a swathe of NE seats in 2019. This speaks of a wider issue amongst voters that will touch on personal economies, personal prejudices, Brexit, job security, access to news sources beyond the mainstream media, demographic changes and countless others besides. It can't just be "oh the boundaries lean towards creating Conservative seats," as I have seen in the run up to this year's boundary review: if Blyth Valley, Leigh, Bolsover, Blackpool, Carlisle, Barrow, even Burnley are voting Tory, it's far more serious and deep-rooted than "oh, it's clearly gerrymandering."