Right,

I removed the vacuum hose that comes out the back of the inlet manifold, blew air down to make sure it wasn't blocked or sucked flat or leaking, and it's all good.

The outer sheathing on the accelerator cable has melted/dissolved along one section, so I cleaned that up.

I removed the TPS and checked the resistance across the pins, and it's right for throttle fully open and closed and it changes smoothly with no sudden jumps throughout the range, so I think that is okay.

I'm thinking the throttle cable is the most likely cause atm, but if it was getting stuck I would expect the engine to rev as soon as I put the clutch in, but it doesn't start to rev up until I have almost come to a stop?!?

I suppose the MAF is the next thing to check, or could be an air leak on the actual inlet manifold or TB somewhere, will have a squirt with carb cleaner to try and find leak.