F25 X3 Not Starting. Press Clutch message, but is pressed. Any ideas please?

[HopefullyHelpful]

Hi all. Apologies as this is my first post and I'm asking for help! My manual X3 (F25) 2.0D 2010 refuses to start.

I follow the usual procedure: Brake and clutch down, press button to start... but it doesn't. The first stage of the ignition comes on ok (lights on dash ect) and the message saying press clutch to start.

Brief background to this: for a couple of weeks prior, the car occasionally wouldn't start the first time (not turning over either), but did on the second attempt. The clutch pedal was also squeaking slightly. I thought it might be connected so had it greased which stopped the squeak. Not starting first time became more frequent (always with the same message) and a couple of times I slammed the clutch down and it started which could, of course, be coincidence. Then it just gave up trying to start altogether.

The X3 is now with a general mechanic. They have replaced the clutch sensor switch and checked the starter motor and battery etc. The two original separate key fobs have been tried. An auto electrician cannot find any electrical/wiring faults and there are no fault codes showing. Apparently he did manage to get it to crank but not start a couple of times. They have now run out of ideas.

Has this happened to anyone and been fixed? Or any ideas on what else to try please?

Thanks for reading.