Eurostar is offering 30% off their premier seating for trains this spring if you purchase by November 30th.
Since it was only $5 more then the 2nd class on my train I booked it (my return is in 2nd, the cost there was $50 more)
If like me you haven't booked and have apparently decided to travel on a busy day where more organized travelers already got the cheap fares, this might not be a bad deal.
(Decided this past weekend to go to Paris in March to run a half marathon... could not get a good deal on a frequent flyer ticket to Paris so am flying in and out of London with nights in London on both ends)