I had a similar incident a while ago on the M1.
Weekend so not busy.
Slow car in lane 1
I came up behind (at 70 in the Morgan).
Looked in the mirror - in the distance in lane 3 (for no reason) was a GTI Golf doing a loonatic speed.
He was not indicating.
So I indicated and pulled into lane 2.
We were on top of the next junction and what I couldn't know was that he was intending to go off there, so he came past at at least 90, with his horn blaring, then cut sharply across and just made the sliproad.
Hopefully the speed cameras got him on the way.