Hi everyone and thanks for the replies. The hand crank turns fine and the needle and bits move freely. All the knobs and buttons turn OK except for the round one above the red slidey knob... On the back of the manual someone has kindly sketched a wiring diagram, so might be handy

I shall have another read of that as I am sure that explains how to re-oil it and stuff, once the musty smell has gone.
This is one of two sewing machines I 'rescued' - the other is a 193(6?) manual Singer (quite a common one) with a lovely wooden case, also not opened for many a year, again, probably my Gran's
At the weekend, my Dad had a clear out of his new loft and found.... an electric Singer sewing machine... looks like I may form a collection!!