An update on this, it looks like the problem is with the right-hand drive shaft inner CV joint. There's an awful lot of play in it, lucky it hasn't flown apart at 70mph.

How old is the battery.

Have you checked the volts.
See below.

A healthy 12-volt car battery should measure around 12.6 to 12.8 volts when the engine is off. When the engine is running, the voltage should be between 13.7 and 14.7 volts due to the alternator charging the system. A reading below 12.2 volts indicates the battery is significantly discharged or damaged.
Check with multimeter..

Also, is it a stop start or normal battery as I've seen reports on other forums that stop starts don't recharge/hold charge succesfully if they have drained.

If normal, might be best to remove and do a full recharge off the car.

... there's no buzzer if he leaves his lights on!

Different models in different countries, so I'm not confident what you should expect. If you find a buzzer is the best solution, let me know and I can talk you through implementing one.

If I remember correctly the lights are left on for a time period, after one press of the lock button "HALO" and if you double press the lock button they all turn off. Also if you remove the key and turn them off then back on, they will leave the marker/ home lights on, so you can leave the car with a little illumination. This will still drain the battery after a while though.
However if your car has had some electrical gremilns, I would test these features to make sure they all still function.

Hi all, new owner and first post, bought my 17 y/o son a 1.4 Comfort, 125000m great condition full DSH so on to a winner, had a couple of electrical gremlins with interior lights shorting the weird double fuse thing in the drivers side fuse box. I've also noticed there's no buzzer if he leaves his lights on! going to be a problem as I'm driving at the moment and my normal car has auto lights so don't have to worry lol. is there something kissing/broken or does the car not come with one? TIA