Travel by Train in France and UK

The easiest way to get from Rennes to London is to take a through TGV train to Lille Europe and then change to the Eurostar to London. You may be able to get cheaper fares or a more convenient departure time by travelling via Paris, but this will mean a trip across Paris on the Metro (you can get Line 4 direct from Montparnasse where the Rennes train arrives to Nord where the Eurostar departs, but it still means buying an extra ticket and hauling luggage up and down stairs). Book the ticket from Paris or Lille to London at www.eurostar.com. Book from Rennes to Paris or Lille at www.tgv-europe.com, but claim to be in Canada or the UK and ask to pick up your ticket at the station or print it at home. If you book 90 days in advance you get significantly cheaper tickets although these are strictly limited to a specific departure time. Expect to spend most of the day on the trains.

Dianne - Since you didn't specify date I used January 24th. Looking at the TGV Europe website I found a train that departs Rennes at 6:07 with a change at Lille to connect to London for 296.00€ for the family. There is also a train departing Rennes at 9:33 am arriving PARIS MONTPARNASSE at 11:39 then you'll have to transfer to Gare Nord for a train departing at 13:13 arriving London at 14:39 for 276.00€ for the family. Also if you decide to purchase tickets on TGV Europe specify Great Britian as your Ticket collection country otherwise you'll be sent to the Rail Europe website. I hope this helps in your planning.

That might be a bit of a tight connection to get on a Eurostar. Remember that Eurostar has airport-style security and passport checks and the company themselves say you should check in at least 30 minutes before departure. I haven't used Eurostar from Paris for a couple of years but other people on the helpline have reported long waits at Gare du Nord recently.