Brittany Ferries sails from Plymouth in to Roscoff. There are also sails from Portsmouth to St Malo. I have a discount code if you are coming by Ferry.
Flybe flys from Glasgow to Rennes or to Brest. It also flys from Southampton to Rennes.
If we know in advance we can arrange to pick people up from the airports. I know the Thursday flight into Rennes is looking like a popular option as well as the monday flight returning.