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The rule of thumb is that because no vendor will give a surveyor permission to conduct an invasive survey they put any potential problem, no matter how small down as something along the lines of "requires further investigation". They do this to cover themselves from a legal standpoint.
If I were you I'd want to Quantify how much remedial works will cost. As you have already said it is not in your interest to get a free quote firm to quote for this. I know someone who is good at this type of thing (he's a registered surveyor in remedial works) but he's busy and normally only works in and around Ealing. If you want I can ask but the answer will likely be no.
Where is the house?