I have already had a Mortgage Valuation. Is there any point of having a further survey done?

You would not buy a car without inspecting it physically and checking the service history. This is similar for properties; the difference being is that this is potentially the biggest investment of a lifetime.
It would be of immeasurable benefit to know what issues may occur in the short and long term and have a plan in place to cover the costs for these. A valuation focuses on the price of the property, whereas the building survey focuses on its condition. Realizing you have moved into a property wrought with problems can be a nightmare, so don’t let it happen.