Why are we blaming the french? they didn't vote for Brexit and aren't responsible for increasing/paying for extra capacity at the French border posts on UK soil.
Stamping passports is what happens to 3rd country nationals & that adds time, a lot of it, when dealing with 100s of '000s of passengers, plus having recently been to France, i ve seen UK people arguing with French officials because they don't want their passports stamped!
The UK seems incapable of organising anything at the moment, the numbers travelling across the channel is entirely predictable and delays we are now seeing were talked about pre 2016, i remember seeing the graphs on how long the queues would be for just a few seconds of delay for each passenger.... all Project Fear.