Eurostar from Paris to London all in one day

Yes its only 2 hours and 35 minutes city center to city center. You can enjoy a full but quick one day visit.
To make it reasonable book as early as possible,, tickets only increase in price. Use the Eurostar website , not RailEurope, use UK as your country of residence or you will be switched to RailEurope and pay more. Take a snack on the train, food not great, and everyone packs a picnic. Book second class if money is not growing on trees for you, its very comfortable . Look at different days of the week for booking to find cheapest ticket, usually tues-thurs.

I would recommend checking BOTH the Eurostar and Rail Europe website. I booked my round trip to Paris from London a few weeks ago. Checked both sites, did the conversion from Pounds to Dollars and... Rail Europe was $15 cheaper (and that included the booking fee) I fail to understand why folks blindly assume "Rail Europe is always higher"

Well Carol,, its not because people blindly assume it, its because in 99% of cases it is true,, and mostly because the RailEurope site does not offer the full schedule, so there are usually cheaper options on Eurostar..( different days and times can be priced differently) . You were lucky . How much did you pay?

The cheapest ticket is $59.00 each way every day of the week and every departure time. However, there is an allotted number of discount fare tickets at each price level for each train. When the quota for the cheapest tickets is reached, the price goes up to the next level. That is likely to happen sooner on weekends than on weekdays.

Entered the date July 17th on both sites, same departure time ( 7.01) same return ( 20.13) on Eurostar total was 69 GBPS,, on Raileurope it was 75 GBPs , plus 4 for "booking fee" .

"Entered the date July 17th on both sites, same departure time ( 7.01) same return ( 20.13) on Eurostar total was 69 GBPS,, on Raileurope it was 75 GBPs , plus 4 for "booking fee" ." Myabe you shuld try it in dollars? Because I just did the same trip on both sites Rail Europe July 17 Paris to London $118 plus $6 booking fee equals $124 I can't find the 69 GBP fare you found, but even if I did a quick currency conversion brings that to $109 plus the 4 GBP to book via credit card ($6) brings the total to $115. And the currency conversion rates I check are not the ones most of us will get (banks are not as generous as traders) While this one comes out in Eurostar's favor if I book the fares I can see on Eurostar (80 GBP) it comes out in Rail Europe's favor. That's why it pays to check everyplace. And actually since OP is going Paris to London then he should also check TGV.

Looking at TGV for same date,, cheapest options were 44 euros each leg.. so 88 euros. I am not aware of extra fees for paying by cc , I just bought some tickets from diTGV and paid no extra fees.. must be built into higher fares. Usually Eurostar is cheapest when booked far in advance. Just been my experience, not an assumption as I always compare and search for best deals. Carol, I book in Euro to be charged on my credit card is euro, it is a better deal then doing that conversion. Just like hotels, always ask to be charged in euro, never in dollars.