That's for you help, very helpful to know it's 5% with the ability to claim in back at the end of the build.
We are making progress on site, removing both asbestos roofs and the roof supports, just leaving the blockwork walls. It appears that the block work is in fact hollow block and in areas is in particularly bad condition, so much so that in some areas it would have to be rebuilt. This has lead me to reconsider my construction approach and I am now considering demolishing both structures and replacing with a SIPS structure which works out easier, cheaper and results in a more efficient build.
I have checked the approved planning documents and I cannot see anything stating that the existing structures must be used however it is a 'conversion'. I will discuss further with my insurance and mortgage supplier but do you foresee any issues with this slight change of tact? The finished property will visually look the same.