Eurostar Paris/London Day Trip Worth it?

I have never done this as a day trip, but I have taken the eurostar between the two cities. Yes, you just show up a bit early and off you go. It's a very easy trip. London is a great city that is worth a long visit, but I think you can get a lot out of the 11 hours you'd have. It would just take some research into what your top priorities are, how to get between them, and the time each takes. Is there a specific site you're interested in, or more getting a sense of the city?

Definitely doable. We have done it a couple of times but then, we have previously been to London a few times staying a few days. You will need to decide beforehand what it is you want to do and see and plot your day. London has plenty to offer.

I personally think it would be worth it, just choose one or two sites and don't try and cram too much in, I totally recomend the Tower of London, it includes a free Beefeaters tour and they are hilarious.. very interesting.
The trip itself IS easy,, bring your passport , and off you go.. take a snack onboard if you like the stuff in the bar car is pretty horrid. Its only 2.5 hours and pretty comfy in 2nd class..

As long as: You don't mind the price of the tickets;You can accept that due to limited time, you must be ruthless in deciding what to see, and totally accepting of what you don't see;You are not "taking time away" from Paris (in other words, not skimping on things you really want to do in Paris).
then, you certainly can do this and say it's "worth it." But, if all these conditions are not met, stay in Paris (and environs), and see London another time.

Totally doable. I know some people recommend the HoHo tours as a great option for a day trip. My mom and I were going to do the same thing next month, but we decided we wanted to do have an afternoon tea and also have a nice dinner so we decided to stay over one night.

We did the opposite several years ago. We had 4 nights in Dublin and 2 in London, overnight Paris, and back to the same hotel for the last two nights in London. We arrived in Paris at 10am with only a small daypack with what we needed to overnight, (left the luggage at the hotel in London). Had a very full day of sightseeing, then we had a nice dinner near our hotel and Eiffel tower. Following morning we made one more sightseeing stop and coffee at a cafe before catching the 10 am train back to to London. Plan your day in a circle of sightseeing, then certainly dinner in an English pub. The only let down in Paris was that I expected to hear the "Parisian" violin music like you see in movies.......and didn't. But we had a fabulous 24 hours. (followed Rick Steves advice for the overnight, and wondering if he maybe mentions a similar excurion from Paris to London on the Eurostar.)

As others have said, it's certainly do-able as a day trip. However, if you like theatre, spend one night in London so you can take in a play or a musical. If you can't spare a full second day in London, you can take an early morning Eurostar back to Paris. On weekdays the first train departs at 05:40. On Saturdays it departs at 06:18 and on Sundays it departs at 08:20.

I would do it, but only if you can spend a night. Otherwise it's a lot of money and effort to get such a slight taste of London. Since you have 2 weeks in Paris you could allot 2 days to London and still see quite a bit in Paris.

Of course, one day isn't going to be enough. Is one day in any city enough? But, why not go and get a taste of London. It's a great adventure. You could go on a "hop on hop off" bus tour of London. I enjoyed this concept in several cities. There is also the Original Tours of London. Like others have mentioned, determine your siteseeing priorities. Note that the museums are free. Have a great trip!

If you do go, check the weather in London for the day. We did this trip in mid-June 2008. It was hot in Paris and we were caught unaware weather-wise in London where it was cold and rainy. We did purchase a travelcard for the day and used it not only for the tube but the red double decker buses. Surface traffic was terrible in places and we could have walked faster. So we got to see some of London that we have not seen before and still had a good time.

Wow, thanks for the confirmation! We are going to give it a go. Now one final question, if we plan to spend the night could someone suggest an area or a hotel that is reasonably priced? To be two hours away and not take advantage of this opportunity seems too good to pass up.
Thanks everyone.