You are definitely getting muddled here.
If Planning Permission was required and you didn't get it, the remedy is typically to apply for retrospective PP. Except that, once a new structure has been up for more than 4 years, the Planning Authority cannot demand that it then be taken down again. However that is unlikely the satisfy an eagel-eyed solicitor who will advise his client (the buyer) that you (the seller) needs to apply for a Certificate of Lawful Development. This is issued by the planning people, but it 'regularises' the structure so that the planning department know it is there - make it lawful. A CLD is obtained by making an application very similar to a Planning Application, the only difference is that the planners cannot refuse it - because it has been there for so long (4 years) that they have no legal basis to demand its removal.
That is probably what you will be asked to do.
It is just possible that your conservatory requires Building Regulations approval. However, since conservatories are regarded as non-habitable structures, most do not need BR approval unless:
1) It is bigger than 30 square metres in external floor area. That's a pretty big conservatory. Or -
2) You've removed the original patio doors separating the original house from the conservatory. If you've done that, all the heat from the house leaks into the conservatory then out to heat the neighbourhood and the house fails the thermal insulation regulations. It is extremely difficult for a glass-roofed conservatory to be constructed to meet the the thermal regs. You best bet is the replace the patio doors.
None of any of the above has anything to do your any warranty the constructor may have given you. Such warranties just assure the materials were appropriate and that it won't readily fall down in the first 10 years.