Boot well was just slightly damp today, but carpet in both nearside footwells is wet. In short I don't think water is getting in around the hatch. The windscreen seal is bowed out at the nearside, which must be the source. Garage said they pushed it back in the other week when it had MOT and service, then they sprayed water around and didn't see any coming in. Well the seal must have sprung again, but in any case the windscreen now has a crack so pointless faffing with a seal! Wifey didn't know when or how the crack happened but when prompted she did remember going over a bad pothole!
So, Autoglass booked to replace the screen on Thursday which fingers crossed will sort the leak. AFAIK they have to replace the seal as the old one generally gets damaged when removed.
I think I'm getting to the bottom of the buzzer/alarm/tone. It's either a dodgy microswitch or the wiring as it goes in to the hatch (a common failure point). I went out this morning, started the car, no tone! I then tried the boot while the engine was running, and got the beep! It was only beeping when the switch was pressed. This rang a bell (as well as a beep!) from the manual. If you try to open the boot from outside when the central locking switch is on you get this alarm tone. So looks like there is an intermittent connection issue. Probably not helped by the damp and condensation. If I can get access to the switch this afternoon I'm going to try a squirt of contact cleaner.