I would have a word with your local police station. I think they might take a dim view of someone blocking access.
If you do this, though, any hope of a pleasant solution will have vanished.
However, it doesn't sound as though being pleasant is getting you anywhere.
If you get no joy from the police, or do not want to involve them, try the Citizens' Advice Bureau. they will have heard it all before and will know exactly what can be done.
It's a rotten situation and, loath as I am to say this, sometimes you just have to move to get away from inconsiderate neighbours. I seriously doubt that they will change their ways.
Sorry to be so negative, but I have had a similar situation. We moved.