Just on a cautionary note...............
The Cert. of Compliance is needed not just "unfortunately" for the mortgage company, it is a necessary part of a property's title, the lender wants it now for completeness but on any future sale, it will also be necessary.
It confirms that works required /or did not require planning permission and that the works were carried out in accordance with pp ( if necessary) and also ( whether pp was needed or not) in accordance with Building Regulations.
It seems that the original person who drew up the plans etc.,etc is not qualified to give a Cert. of Compliance when the works are done. It is an object lesson - there is no point asking someone to draw up plans and apply for pp if they cannot at the end certfiy the works. There are lists of people who are recognised ( by conveyancers/lenders) as qualified to certify.
There may be architects/engineers/surveyors out there who are willing to certify someone else's designs/ building works where they have not been in any way involved but why would they put their own necks on the block?
mf