Brittany Ferries (www.brittany-ferries.co.uk) links St-Malo and Roscoff (both 90 mins from Seglien) with Portsmouth and Plymouth.

Direct flights into Brittany are from airports throughout the UK.
Airports in Brittany are:

Lorient (45 minutes from Seglien) with www.aerarann.ie

Dinard (90 minutes from Seglien) with www.ryanair.com

Rennes (90 minutes from Seglien) with www.flybe.com

Nantes (2 hours from Seglien) with www.ryanair.com and www.aerarann.ie

Brest (3 hours from Seglien) with www.ryanair.com and www.flybe.com