We had this problem – solicitors and “party wall surveyors” trawl the planning applications and then write to the neighbours impacted.
Our neighbour isn’t terrible worldly wise so just signed and returned the letter she got offering her free advice to protect her property and the first we knew of it was when we got a letter saying she had instructed the firm.
As a starter they required:
Payment of an initial fee estimate of £6500 + VAT
Mileage at £1.35 per mile + VAT for the 45 mile round trip from their office to our neighbours house
Soil samples and other geotechnics (estimate – another £5K) before they would give permission to proceed.
It was a complete ball ache and interesting to see that at least in some cases “regulated professions” are actually operating using borderline fraud and intimidation in order to generate fees. The party wall act doesn’t help because the way the legislation works is that you have no choice but to pay any professional operating on behalf of your neighbour, and there’s no test of “reasonableness” when it comes to fees.