Do not have first hand knowledge. I did not attend the Festival of Britain; my excuse, I was six at the time and living in Kenya !!!
However I am pretty certain the a/c exhibited was an original a/c. Two survivors exist:
Supermarine S.6A N248 now at Solent Sky Museum in Southampton.
Supermarine S.6B S1595 now in the Science Museum in London.
For a long time the S.6A was painted as "S1596" so have a feeling the a/c in your photo is this one. Confirmation anyone ???
Planemike