Or something more sinister?

Recently the old girl has taken to not spinning the starter motor on the first turn of the key, however shutting the key off and trying again gets her to start..

It isn't happening every time but it's an annoyance!

Cheers gents,

Does it go click or nothing at all?

No clicking it is completely dead, however shutting the key off and retrying and she's up and running!

Some people I've read say it could be the fuse box, however what difference would turning the key on/off do to a faulty fuse box?

Bad connection, doesn't always make. Or the starter relay in the fusebox.

Even the 'start' connection at the ignition key switch?

Before I knew problem fuse boxes were a thing on P38s I was called out to a Rangerover specialist to diagnose a problem that saw the engine would crank but 9 times out of 10 wouldn't start, the problem turned out to be due to an issue in the fuse box, the relay that powers the petrol injectors positive wasn't switching and it wasn't the relay at fault. Until then I didn't know that the relay coils got a constant positive and were earthed by the ECU (at least that model/spec P38), seemed there was a break in the fuse box between the ECU negative signal to the relay and the relay itself (iIrc or it could have been the relay got the switched negative but not the constant positive). Anyway I wired up an easy get-around once I'd identified the problem. The P38 was converted to LPG but the nature of the problem was more of a job for an auto-electrician than for myself, but I sorted it anyway and was a bit surprised that none of the staff at the specialists could solve it.