Engine cuts out when put in gear

[unfazed]

To be honest I really don't expect it to be a mechanical fault due to one test that I did

- Engine off, in 1st, clutch pulled in - won't start

Bike has to be in neutral if the the side stand down to start.
With the bike in gear, the side stand must be up and the clutch must be pulled in to start.
Since it starts in neutral and the side stand tests correctly then the next test must be the clutch switch
Bypass the clutch switch by removing the wires to the clutch switch and connect them together with a piece of wire.
Does the engine start? If it does replace the clutch switch.