It's not their greatest offer ever, but Eurostar currently has excellent availability on £36 singles (£72 returns) between London St Pancras and Paris. All in, generally much more convenient than flying: http://www.eurostar.com/uk-en/calendar/find-your-return-paris
One of the less known facts if Eurostar are the industry perk rates, twice this summer I have enjoyed hops through the channel @ £59 each way premier service. Access to the lounge is not included, seats have to be booked a minimum one week in advance and choice is quite limited close to T- 7 days, but you can usually find something if you travel around lunchtime. For some this is a most pleasant way to hop across, and it gets all the more tempting with the rate of the Euro showing weakness.
Ashford and Ebbsfleet departures have similar good rates. Useful for those of us who have a closer International station. (Not that I've ever taken the Eurostar, despite living 1km north of the UK portal and working in the St Pancras area).
Eurostar currently has excellent availability on £32 singles between London St Pancras and Paris, Lille Brussels ( I tried to post a link but it seems non permitted until I have more posts )
