The most convenient means of travelling by train from London to Brittany is to take the  Eurostar   and change at Lille; this avoids having to change stations in Paris, which is either an extra expense, or a hassle and a bustle, or all three. Changing from a Eurostar to a French TGV in Lille just means changing platforms, and sometimes not even that.

In early 2008, the most convenient departure is the 9.53 from London St Pancras, which gets passengers to Rennes at 4.07 p.m. local time. With connections at Rennes, Quimper can be reached at  6.54 p.m , Saint Malo at 5.42 p.m. (by local train),  and Brest at 6.27 (by changing to another TGV).
For timetables and to book tickets, click here for the Rail Europe site .

For the return journey, the morning direct TGV to Lille leaves Rennes at 9.15,  meaning an early start for anyone coming from deeper into Brittany;  but this lets travellers reach St. Pancras  by 3.56 p.m, leaving plenty of time for connections to other parts of the UK.. However, given the early start required for this service, and the longer-than-necessary wait at Lille, it may be easier, for the return journey, to check out times via Paris.

Train and drive to Brittany involves taking the Eurotunnel shuttle, then following the motorway via Abbeville and Caen. Parts of this motorway are toll-free, as are the dual carriageways after Caen.