Don't , like I said last time, get a 'valuation survey' done. This is only for the Mortgage Company's benefit and offers YOU the purchaser little protection later down the line.
If you seem to get the 'green-light' from your Estate Agent, arrange an for an independent 'full structural survey' and ask for a valuation from the Surveyor. Should the purchase proceed and defects come to light, you may get recompense from the Independent Survey, you certainly WON'T from your mortgage company.
Your mortgage company ought (that's only, ought) to accept this as evidence of the value of the new property.