That looks different to the Mantel box that i know of, looks as if there is far more room in the CU area of the box.Also looks as if it's already been modified to some extent too, with the inclusion of that RCD main switch. You would never have been able to fit that main switch in the Mantel box that i changed the CU skeleton in.
Batty,
As far as i know, Crabtree won the contract to produce the split load CU skeleton frames for these council house Mantel boxes ....so unless Wylex as since produced a similar fitting frame, Crabtree were the only ones to produce them. very lucrative for them i would imagine too, going by the amount of council houses that were fitted with these Mantel box arrangements.
But i'm way out of date with the going's on in UK these day's ....Not surprised anymore, with anything that happens within our industry there now, ....They sure seem to have made a complete pig's ear of the supply companies, since the demise of the old leccy boards ...lol!!!