Don't you still have the remaining manufacturer warranty from the time of original purchase? (not your purchase from OcUK).
I have all the warranty information for my B-Grade monitor (Samsung) and i'm sure if i called them they would look on their system to see the date it was sold and take my warranty from that date.
So while you don't know how long the warranty is, i think it would still be valid.
Maybe i'm completely wrong though.
The Dell monitors in this offer were never sold with any Dell warranty.
OcUK bought them cheap without any Dell warranty so the only warranty is with OcUK.