Toilet Cistern Lid

If there are no identifying makers marks on the wc/basin anywhere then take a photo or two on your phone and go to some of your local bathroom showrooms and look for the seasoned members of staff. The last 25 years or so has seen a flood of cheap foreign made bathroom delph come into the country and a lot of it has little or no markings, the best option maybe just to try and source something that resembles what you currently have, in that case take the lid with you. Failing that it will be a new cistern which isn't to big of a job/cost, should take a plumber no more than an hour to swap out if you have it sitting there for him.