Ok, I've been doing some more digging and Googling... Are there any professionally installed alarm systems that work on Apple's Homekit standard? Or is it still too new? I can see some DIY kits, but I really want something a bit higher level than those.

The HKC app and the Risco app can be programmed to work wireless outputs, the can be named on the app ie lights, garage door, curtians, ect then from the app on your phone you can control the outputs. I already had Lightwave RF home automation kit in my house, so I wired the outputs into a preprogrammed remote control. Now my lights come on when I open the door and switch off shortly after I disarm the alarm, I can control the lights, curtians, and heating from either app lightwave or HKC. Potentially all systems with apps can do this. Your panel is a Castle Meridian as others have already mentioned

Ah that's interesting. Some google work suggests that LightwaveRF are also working with Apple to make their stuff Homekit compatible, which would then be a great solution.

So now I just have to find an alarm system which looks like it will be Homekit compatible too...

Ah that's interesting. Some google work suggests that LightwaveRF are also working with Apple to make their stuff Homekit compatible, which would then be a great solution.

So now I just have to find an alarm system which looks like it will be Homekit compatible too...

You wont find one, least not a good one. You need to find an installer clever enough and willing enough to do it for you, if you were closer we would do it we love doing the out of the ordinary.