Do anyone have an idea on how arrivals usually look into London around Xmas?

If I would stab wildly in the dark, my assumption would be that foreigners fly out ahead of Xmas, and return after. Hence a lot more inbound traffic after Christmas?

Obviously a lot of Brits living abroad, but my guess would be that they do not return to the UK ahead of Xmas to the same extent as foreigners return after? So after my wild stabbing I'm thinking that it might be a tad more crowded at the border on the 26th and onwards?