Have they? I just asked Google “How has the EU made it difficult to Britain to leave?” and found no evidence.
Just another point – If you think the ‘illegal immigrant’ problem is bad now, due to our total lack of planning, for the first six months of 2021 the UK are only going to apply ‘minimal checks’ on lorries entering the UK (mostly lorries carrying medicines, alcohol and tobacco) and have to wave the rest through unless they want 10,000 lorries every day creating 7 mile tailbacks every day. This fact has been well publicised – I’m sure they know about it on the other side of the Channel and why the hell should the French bother stopping them now? At least they used to make some effort (remember all those Camps – The Jungle, etc?) but now we’re out of the EU it will no longer be a problem.
France will be checking every single lorry entering from the UK.
https://www.bbc.co.uk/news/world-europe-46064836