A classic 531 front-ender...
... The over-engineered fork transfers the impact to the top-tube and down-tube, presumably just beyond the butts in the tubes.. so I heard.. not talking from first-hand experience, well, not with 531, anyway.
Maybe green frames really are unlucky? and somehow it often seems to be Mercians that get photographed in this state... wasn't there a yellow one a few months ago?
Year of manufacture should be either the first two or last two of the serial number, if there is one.. '70s?