Those planning to compete at San Sebastian in March will want to do a couple of lower-profile indoor races first. So far I only know about three, all at Lee Valley :
Sunday 27 January : London Indoor Games : 3000m : closing date for entries 21 January : more details here.
Sunday 10 February : Essex / Eastern Counties / Open meeting : 1 mile : closing date for entries 10 January : more details here.
Sunday 17 February : Vets AC / Southern Veterans Championship : 3000m : closing date for entries 26 January : more details here.