There's a banner ad currently on the SNCF website (choose the British flag, not "Rest of World"), saying that all fares purchased today (Wednesday French time) are 25 GBP off. Alas, I'm not ready to buy any tickets yet, but perhaps someone else is. Seems like this could save a great deal for someone buying tickets for a family, in particular.
The banner also says there will be "A new deal every Wednesday throughout February".
Happy shopping!
Edited to add:
I'm not seeing that banner on the direct English-language site, so I'm not sure what's going on. I haven't tried comparing prices.