Remember if a local trades person does not do work above a certain amount per year (£82,000?) they they DONT have to be VAT registered and DONT have to pay VAT on a job.
IF they ARE VAT registered they have to place their VAT registration number on a quote.
IF they are NOT VAT registered and add VAT on the bill afterwards then it is a scam.
Found this on the web:
"If the tradesman is VAT not registered, then they cannot add VAT. If they didn't mention their VAT number on their quote (which they should do if they are VAT registered) then this reduces your risk, but it's probably better off to confirm with them"