Hi Dibs-H I have been watching these posts with interest.
I work as a surveyor for a Local Authority and have to apply on behalf of the Council for a Party Wall Agreement. For example we need to replace a roof which is next door to an ex Council property sold under the right to buy scheme.
There are three approaches
1) As a good neighbor you should always inform your neighbor of your intentions and set out what you are proposing to do, whatever. Nothing upsets a home owner more than when the first awareness that something is happening is when workmen, waggons or scaffold turns up. If you are working within 1 meter of the party wall you are obliged to inform your neighbor in writing and if a gentlemans agreement can be reached both copies of the agreement should be signed without prejudice of what was discussed. In the event a disaster occurs the Judge will assess on who is acting reasonably.
2) Because of regulations for example ensuring say the fire breaks are installed correctly I have to act as the Councils Party Wall Surveyor this service is offered free to the neighbor and if agreeable a letter confirming this and is signed by all parties confirming this agreement.
This is the most frequent process.
3) We go down the full Party Wall Surveyor agreement I still act as the Party Wall Surveyor and deal with the neighbors party wall surveyor. The neighbor may be a landlord, developer, business or as in your case a church body acting as a charity.
Employing Party Wall Surveyors is expensive and if employing one should not be done on the cheap. As well has purchasing knowledge and experience you are also obtaining his indemnity assurance.
A member of the R.I.C.S. ensures this. Costs depend on the size of the job and I would take £1,000.00 as a minimum