Engine turns but doesn't fire

Hi all - I have a rare late soft-top with a VVT engine and yesterday it refused to start although it was turning over quite happily. No previous issues - it's been running fine. Also no engine management light or anything showing on my OBD app. Looking around the forum it seems this is commonly caused by a faulty crankshaft sensor, but I'm reluctant to splash out on one unless I'm reasonably certain it will fix it (quite apart from the fact that it seems to be a bit of a b*gger to get at). What else should I check first? Can the sensor just fail overnight? The fuel pump appears to be running OK if the whirring I can hear through the filler pipe is anything to go by. All suggestions gratefully received.

Is the padlock symbol on.On the clocks
When it's turning over

If you have an app that can read fault codes you should be able to see some sort of data list.
Looking at the data list you should be able to read the engine rpm. If the figure does not change then its possible the crank sensor is faulty.

I, personally think you are jumping the gun a bit.
Are the spark plugs sparking?
Is the fuel actually spraying good fuel out the injectors?
Perhaps its just flooded?

Start with the basics, can you smell petrol under the bonnet after turning it over for a bit? That would indicate the engine has flooded.
No fuel smell, is fuel getting to the engine? Electric fuel pumps run noisier if they have no fuel to pump.
Before you risk spraying fuel all over the engine bay, remove the spark plugs. Are they ok? If not, when were they last changed? If ok, check for a spark.
No spark = cam sensor or crank sensor or immobiliser problem. Sparks = Possible fuel issue. Check the fuses (all of them!) to make sure injector drivers/ecu feeds are all ok.
THEN, if you need to remove the fuel pipe at the fuel rail, point the pipe into a jar or something and have an assistant turn the ignition on for a few seconds.

Searching the forum/googling and apps are great for additional information but you have to start with the basics.

Nope, not an immobiliser problem. I have a second broken key that I tried, and that flashes the padlock light which the main key doesn't, so I think I can rule that out, but thanks anyway.

Thanks for this detailed response - I'll run through this tomorrow. If it's flooded, I believe the old carburettor method of clearing it by flooring the accelerator doesn't work any more so how do you clear it? Also it misbehaved immediately on trying to start from cold so never had a chance to flood I would reckon. As for the plugs, would one dodgy plug produce these symptoms? It seems unlikely that all four have failed simultaneously. But you're right, checking for a spark will narrow it down so thanks again!

I might be wrong here but i am sure if you hold accelerator pedal to floor and try to start it
the ecu doesn't allow any fuel through so in theory this would clear the flood