All part of the rich tapestry of British driving. I followed a BMW X7 onto the Motorway last night doing the same thing. 6pm so busy and and I in my wife's Toyota Aygo (Three cylinder 1000ccs of throbbing gutlessness.) Me doing my very best to get the Aygo beast up to 70mph, catching said BMW at a rate of knots as it pootles, no signal and not using the mirror into the left hand lane causing cars already in the lane to brake, swerve, and general mayhem to ensue. So I brake on the slip lane to 35mph

. Slip in behind the car that left smoke from its tyres braking for the BMW and strat to accelerate again. We all get up to 55mph and I take the chance to pull into the outside lane (There are only two.) and accelerate up to 70mph, only to have the BMW, still at 55mph pull out in front of me and I'm braking again.

We tootle past a lorry and the BMW is still in the right hand lane and now roaring along at very nearly 60mph! A long gap in the left hand lane so the BMW stays right and only pulls in when we have nearly caught the next lorry. BMW pulls in I scream the Aygo in 3rd up to 70mph and pass, and the BMW chops into the right hand lane behind me causing flashing lights from the first of the stream of cars behind me.
Now I realise I'm privileged to be allowed
to use be anywhere near a Motorway when a BMW wants to use it but even so...