Thanks all
just had exactly the same problem with my VVC. Glad I realised it was probably the plug before I stripped out the speedo cluster. Turns out the plug wiring had just been "helpfully" strapped aside with a cable tie during a clutch replacement. I bought a spare loom a while back to upgrade to electric mirrors so was easy for me to grab a spare plug and graft it on.
However, if anyone ever needs a new plug, I believe they are called
Junior Power Timer onnectors, can be bought as a kit with a boot and contacts on eBay for £2-3 each.
e.g: