Following on from the Eurostar cash sale 2 weeks ago, there's now one in conjunction with everyone's most boring loyalty scheme - Nectar!
As far as I can tell, it's available for pure-Nectar redemptions, or for mixed Nectar + cash bookings. The minimum nectar points used is 500 (£2.50 off), so even if you don't have many Nectar points you can still take advantage
For Paris, Brussels and Lille, it's "from" £58 for Standard returns, £109 for Standard Premier returns. Any Belgian Station (so Bruges, Antwerp etc) is £70 / £125. The ski train and south-of-France trains seem to be excluded this time, sadly. Booking is needed by the 28th of January, though the cheapest seats will likely all be gone by then.
Took book, or even just to check availability, you need to ring Nectar on 0344 811 0811. No online booking possible, and you'll need your Nectar card to hand, plus your credit card if you want to only part-pay with Nectar
Full T&Cs on the Nectar site, key part is:
This offer is for a promotional fare of £58 Standard/£109 Standard Premier Return to Paris, Brussels & Lille, and £70 Standard/£125 Standard Premier return to any Belgium Station. The £10 Nectar Booking fee will be removed for all bookings made during the promotion, credit card charges may still apply. The offer is valid for bookings made between 14/01/16 and 28/01/16 inclusive. The promotional fares will be available on a minimum 25,000 return seats during the booking period - 15,000 return seats to Paris and 10,000 return seats to Brussels. The offer price is available on bookings for travel taking place between 14/01/16 and 25/05/16