Strictly speaking, if you had changed lanes into the mini driver, it might have been your fault, irrespective of the fact he was speeding.
Lots of cars travel faster than 70 on a motorway, some legally, and you have to make provisions for this.
If you were doing the speed limit ( :wink: ) and the middle lane hog was therefore going slower, the mini driver’s speed differential would have been too high no matter which side he chose to pass.