I am trying to find an old fashioned (I think) kind of door handle that uses a thumb piece on both sides of the door to operate a mortice latch. I remember them on shop doors when I was little (1960's). I have found this description on the web:

Thumb Piece
In the case of door handles that aren't rotating door knobs, a thumb piece is mounted above the handle as a means to slide the bolt out of the door frame. Spring loaded, thumb pieces automatically return to the closed position when pressure is released from them, extending the bolt to hold the door closed again.
Read more: Parts of a Door Handle | eHow.co.uk http://www.ehow.co.uk/list_6746568_parts-door-handle.html#ixzz1Fwey8IUz

And this seems to describe exactly what I mean, but I cannot find any examples on the web to confirm. Please help and where can I buy one in the UK?

Are you looking for something like this? Or are you looking for some kind if thumb latch that you press down like on a gate latch (which I can't imagine working on a mortise lock)?