I have the carcass of a Carlton Corsa (1970-ish) bike from which I want
to remove the forks (thinking might do for wheel truing on a bench).

Please how?

I have loosened a sort of sleeve nut from just below the handlebars, but
not much useful is revealed. Then, below that and (looks like) attached
to the frame is a collar (used to be chrome) and then on the fork end
there is a similar collar. Neither collar has any obvious means of removal.

TIA,

Jon C.