Hi Barry, I trust you're out of quarantine and it's all fixed? I have a under dash handbrake, but I think the answer is more fundamental or generic? On probability, either the cable has detached from the lever, or the inner cable has broken somewhere along its length or at an end. It's a two part cable, I think, so you might have lost the clevis pin at the joint (under the transmission tunnel near the Diff) between the two? It might alternatively have pulled out of the plastic knurled nut adjuster, under the car near the diff too. If you have the time, investigate, if not, speculatively buy replacement cables from Redline, and hope it's not the handle - which can distort and once remove from its mount, be persuaded back into original profile so as to accept and retain the cable end, with some mole grips. Whilst it is off check and grease the thumb-push ratchet mechanism - you can withdraw it from the handle outer. I think the assembly guide recommends three or four clicks to lock the back wheels in operation, from fully home. WW

On a very early Seven with an under dash handbrake, I remember stopping on a hill for a roadworks red light and thinking, this will take a while so I'd better put on the handbrake, which I did.  The lights were red for so long that when we finally had a green, I'd forgotten all about the handbrake and only when I stopped 20 miles further on, did I smell the brake linings.  Anyway after letting them cool down with handbrake off, they seemed fine, actually the handbrake properly worked, so it obviously took the glaze off.

Anyway the point is that after that, I changed to a vertical tunnel mounted brake.  The first one I did used a Morgan flyoff lever, but must have been made by a blacksmith, it weighed so much, after that I used MG Midget items.  It's quite an easy job but means working tight up under the car on axle stands.  I've recently done it again with my current Seven, an ex academy car and it works a treat.  

Well worth a couple of hours to do the job.