Definitely call 999 - crime in progress.
Then lean out of your upstairs window taking photos of the scumbag - it might not stop him, but it's fairly certain that your local NPT will recognise him when they get involved and can go along and invite him for a chat.
I'm concerned about the claimed lack of police officers in some parts of the country overnight. As you'll have seen from
'Traffic Cops - Under Attack' on Channel 5, up here in Yorkshire there are dozens of bobbies driving round in BMWs all night with camera crews in tow...