There is no minimum speed limit, but you could be arrested and fined for driving too slow.
Although driving at 40mph on a motorway you are not breaking the law, you could be causing distress to other road users.
i think there is actually. a vehichle incapable of speed over 25mph isn't allowed on a motorway.
the one thing that should be banned from motorways in my opinion is F**** cranes! crawling along the M3/M27 at 30MPH in the rush hour they are a menace! Lorries should be banned from overtaking on uphill motorway sections as well.
my son had a problem with his car the other week and had to limp along to the services (he was driving at about 50) he got pulled by the busies and told off for driving too slowly! FFS
yet they do naff all about the idiots who sit in the middle lane puteling along at 60! yes 3 points would be a great idea. and if you get caught a 3rd time then banned from motorways for life!