Is there a minimum speed on the motorways and if so what is it? C.M.

There is a minimum speed, but it only applies to vehicles using the fast lane (the one furthest left). You may not drive in it more slowly than 80kph, assuming weather and traffic conditions are normal, there are no roadworks etc.

It is considered dangerous to remain in it after overtaking if you are going too slowly because it may encourage people to pass you to the right, which is against the rules.

The left-hand lane is mainly meant to be used for overtaking only, unless traffic is very congested, in which case it is acceptable for cars to remain in any of the lanes.

In other circumstances there is no precise minimum speed, but the Code de la Route states you should not drive abnormally slowly in view of road conditions, in a way that will bother other drivers. Going too slowly can result in a fine of €35.