Is this a difficult job to do by someone not very well versed in these matters? One of the two hinges has severed and i reckon it may be difficult to unscrew the other one. Should i get a plumber. I know for the average DIY person it is probably an easy task
Its an easy enough diy job if you have a few tools, vise grip, ring spanner, but the nuts underneath may become corroded due to damp and you might need wd40 to loosen them up.
You can get replacement hinge sets but sometimes its easier to just get a new seat.
Woodies do a universal hinge set and probably more specific sets I reckon.
http://www.woodiesdiy.com/Product/Toilet-Seat-Hinges-Pair-of-Universal-Chrome-Plated-Hinges/12944/6.0.0.1