Any ideas how my landlord can get new ones/a new lock, he's totally clueless. If a locksmith is required can anyone recommend a good one in the Manchester area?
If it's a swedish oval (also called Scandinavian Oval) you can probably remove it without a key from the inside, and buy a replacement cylinder the same length.
As mentioned above, if it's a Scandinavian oval, you can remove the two cylinder mounting screws from the internal half without a key. Any Scandinavian oval (sometimes called Swedish oval) cylinder will fit, doesn't have to be trio-ving. Do make sure you get the same length though.