Thanks for your reply.
Well, firstly, you did of course buy the property in its existing condition, so your Insurers are correct in that they won't pay out, as it was an existing problem.
Your only possible claim, therefore, is against your Surveyor-
I would certainly have hoped that your Surveyor would have checked for damp from within the property, and if this was not picked up, you may well have a claim against him.
You therefore need to check the Homebuyers Report- if of course it did mention that there is damp (and recommend a further report be commissioned), then I'm afraid you have no claim and you will have to foot the bill for any remedial works.
If the Homebuyers did not mention any damp, you would then have to prove that it should have been spotted, and make a claim against the Surveyor.
I hope this assists and set sets out the legal position.