What does your fathers accountant say?
VAT on property is one of the more complex areas.
First it is important to establish when the property was completed? If after 1 July 2008 then the new VAT on property rules apply. You father developed the property with the intention of making a taxable supply ie sale.
The letting of such a property is an exempt supply so your father should have paid back 1/20 of the VAT he recovered for each year that it was let.
Property developed for sale by a developer is always taxable on sale as the usual VAT rules don't apply to this type of property.
If completed before 1 July 2008 a whole other set of rules apply.
Seek professional advice from someone who knows your fathers entire situation.