Certificate of permitted developement

I am in the process of selling my house, which has a conservatory which was there when we bought the house 19 years ago. My purchasers solicitors have asked for planning permission. I rang up my local planning dept and they said I need a certificate of permitted development wfich takes 8 weeks and cost £200. I was under the impression from their web site that you didn’t need planning permission for a conservatory, so why this. Totally confused and don’t have 8 weeks

If the conservatory is directly behind your house and less than 40s.m. you dont need planning permission.

When we bought our place our solicitor requested a certificate of permitted development off the existing owner,i.e. the seller, for the extension that had been added. It shows the buyer that, according to Council, the extension was built within the exemption rules. To be honest I never saw it myself but our solicitor said it had been provided. It didn't take 8 weeks from memory, more like 4.

This is an Irish site, I note the OP is using £, rules will be different here.

OP mentions pounds (£) and permitted development. This is not terminology used in the Irish Planning System.
We have exempted development and our Section 5 costs €80 to submit.

Maybe the OP can confirm their location.