Hi Shaun,
I have the same problem (only worse) with my 04 Diesel. Mine won't start on the key at all now in fact I've almost given up trying.
One thing I have noticed is that if I try to start it by cranking there is no smell of un-burnt fuel at the exhaust, even after cranking for 30 seconds which makes me believe there is no fuel being injected into the cylinders. Once mine is running It drives perfectly with no flat spots, smoking or hesitation. I believe the problem is specifically related to the crank cycle because the on board computer won't start sending fuelling commands until it thinks the system is ready to start. Clearly something in that process is not involved in the bump start process (or the easy start), because otherwise it still wouldn't be sending any fuelling commands. If I crack the problem before you do I'll let you know the fix.
A couple of last resort options for getting it started that you may not have discovered yet are:
1. If the road you are on is flat and you've got 30 or 40 feet clear in front of you, put it into 3rd gear, handbrake off, clutch up and crank. This should get you up to just over 5mph at which point depress the clutch, stop cranking but don't turn off the ignition, put it into 1st and drop the clutch. As soon as it fires, depress the clutch and give it a bit on the throttle. This works for me, but you need to get it up to 5mph or just above. It's no doubt a bit hard on the starter motor but probably better for the engine than option 2 below.
2. Final, last resort. The dreaded Easy Start. You have to be very careful to use a very small amount of this because it goes off with a massively big bang and can make the top end rattle horribly if you put in too much. Disconnect the intercooler top hose from the MAP sensor housing and put a very small squirt (and I do mean a very small squirt) of the stuff into the intercooler top hose. Leave for about 5 seconds then reconnect the hose. Don't worry about doing up the jubilee clip at this point. Turn the ignition on and go straight to cranking, Don't wait for any dash lights to go out. If you've got it right the car will start straight away with no sign of any top end knock. If it knocks you've used too much and need to use a bit less next time. Once it's running remember to tighten up the jubilee clip securing the intercooler top hose or the pressure will blow it off once you get the revs up and it will scare the hell out of you if it happens when you are driving along, I'm sure it's not great for the engine but as a last resort it should get you going and if you call out the AA or RAC that's what they will do but they will probably spray a lot more in and give your top end a massive jolt.
