If I remember correctly, the crankshaft pulley has a rubber insert to take up some shock loading and to make for quieter running. I've had one of these where the rubber had gone weak and the pulley was a bit loose on the shaft as a result. The symptoms were very similar to your description. It...

Oops! Sorry, but I missed the most obvious bit of info needed. It's the 3 litre diesel engine. Duuuuuh, my brain hurts!!

I've noticed that my Range Rover doesn't start the same way as it used to. Lately it has been taking a few seconds of starter motor whirring before it fires, but it used to fire almost instantaneously (had to spell check that one!). I thought it could have been a filter being slow pulling the...