High deposits for new builds

Hi,

I am looking at buying a new build flat but have been stopped in my tracks by the estate agent telling me that lenders demand at least 25% deposit for buying new-builds. I asked at Nationwide, and the mortgage adviser had to look it up to confirm that this is the case. Does anyone know if this is universal? It seems really strange that new build flats would be out of reach of most first time buyers? Stranger still that the mortgage adviser wasn't aware of this. Am I missing something here?

Also this new government scheme seems to be on certain properties, is this a scheme bought in to fix the above?

Thanks!