It looks like there may be an issue with the bonnet sensor, does anyone know if this is adjustable or would it need replacing.

A few times after I've opened the bonnet to check levels etc. the car alarm triggered when I locked the car. It seemed to cure itself after a couple of goes but then the alarm went off for no apparent reason at bedtime in a hotel car park! So now I feel I can't trust it and I'm locking the car with the key

I would start with removing the bonnet switch, cleaning and examining it - test with a multimeter that there is continuity when opened/closed and also the connections for dirt, corrosion, etc.

If all else fails then bypassing will work, but not sure how many thieves would pop the bonnet which they still have to enter the car to release so its not a major thing in reality.