For the last week I have been woken up by a car blasting its horn as it
passes my house at around 6am.

Now on Friday night I stopped at the girlfriends. At 6am on Saturday morning
I was woken up by a car blasting its horn as it passed her house!

Coincidence. I doubted it.

A quick look on my CCTV shows the same car that blasts it horn when it
passes my house not blasting its horn on Saturday morning (probably because
my van was not there but parked outside the girlfriends house) and because I
have good audio on the CCTV I can hear it blast the horn as it passes the
girlfiend house two streets away (the timing is perfect for this to be
correct).

I think I know who is doing this.

My first thought was a DIY spike strip. Any other suggestions are welcome.

--
Adam