It's entirely up to you. According to our developer most people just go with the mortgage valuation survey. I'm quite cautious though and having spoken with our solicitor we went for the Homebuyer's survey. Our solicitor has acted in the past for claims against the NHBC warranty for stuff which a survey would possibly have thrown up. I took the view that in the context of the amount of money I was spending less than half a percent of that on a survey was well spent to get assurance that the place was ok.