Paul wrote:
My parents are convinced that they need to sign away several thousands
of pounds on a treatment known as Protectacoat for a house which has
solid brick walls with pebbledashed render - this is at least 50-60
years old and now there is some penetrating damp.

Why is the damp penetrating now and not during the last 60 years?

Do you have a blocked gutter?

Owain