Having a quick web search and it appears to be cable linkages. I'll try and have a poke around if there's a break in the weather. I hope it's something like this and not the gearbox itself!

I whipped off the air filter box this morning to have a better look (not nice weather for car tinkering!). One of the gear linkage cables has its sleeve slip off so doesn't pull correctly, which is obviously the problem. So you guys are right on that one!

Unfortanately it might mean I have to replace the cable which can only come as the set of two and isn't cheap (Honda parts at £££££!). In the meantime I'll see if I can improvise a method of clamplng the sleeve back into place. At least the job shouldn't be a difficult one and something I can tackle myself.

It's a pity I can't attach photos on this forum to show the fault.