I can't find any great information on this, from what I can see passports should have been at least given a cursory check prior to Brexit, but that now the checks are more thorough, so will take longer. However, that doesn't square up with what some of the travellers being interviewed on the news yesterday were saying, i.e. that at very busy times they would basically just be waved through as long as they were in possession of passports.
Either way, passports do need to be stamped now, which they didn't before, so that will take longer.
Maybe things were let slide before in a way that they aren't being now, maybe France thinks it has a more serious duty towards manning the border than it did before, or maybe they really are just doing it to try and 'punish the Brits'.
Ultimately it doesn't really matter, the rules being enforced now are the rules that apply to third countries outside the EU, we can see that this was expected to be a problem because Dover asked for £33m a couple of years ago to get more border infrastructure in place, and the government refused to give them the money. (This has been widely reported over the last couple of days.)
Brexit - whats the difference..... - Page 197 - Casinomeister Forum
There's something else that's interesting here, I've lost track of the number of times folks in this thread have said words to the effect of, 'I knew Brexit would be a bit of a bumpy ride, I knew it wouldn't be perfect, I knew there'd be some teething troubles when I voted for it', and yet whenever we get a concrete, tangible example of Brexit having made something worse, all of a sudden IT'S NOTHING TO DO WITH BREXIT WHATSOEVER mode is instantaneously activated.
It seems to me like, if Leavers really believed in their project they’d say ‘yes, now we’ve left we’re a third country and that will increase bureaucracy and queues a bit, but it’s still worth it’. Instead they just deny Brexit’s a factor at all. It’s almost as if, deep down, they’re in denial about it.