You mention 2 things here - and there seems to be some confusion whether it is one or the other (or both).
Firstly, Planning Permission may have been required and was not obtained. That would be unusual because conservatories are often built using 'Permitted Development' rights that householders generally have. If it is true that Planning Permission was required, then an Indemnity Policy can be purchased to cover the risk that the local authority demand retrospective action (by applying for the necessary permission). In all circumstances when an unlawful extension is made to a dwelling, once it has been in place for 4 years, the local authority can no longer take action to demand its removal. Lastly, it will be impossible to purchase a policy if the local authority has been contacted in any way regarding the possible infringement of planning law.