Turns out that the only people who make exhausts for Alfa MiTos are Alfa Romeo themselves, and they only sell it as one complete part. So to fix a blowing flexi-connection at the front requires replacing almost the entire exhaust (everything downstream of the catalytic converter), and the replacement part costs the best part of £600 (because Alfa). Ouch.
I could potentially get an exhaust specialist to bodge it by taking an angle grinder to the exhaust and welding a new flexi-connection in, but it's easiest to just let Halfords crack on and replace the whole unit (plus I'll hopefully avoid having to replace the rest of it in a year or two). The replacement does actually come in two pieces but you can't really replace them piecemeal at first because the factory-fitted exhaust is one single lump.
The Gnu suggested getting the engine mounts looked at as well as a flexi-connection failing could be a sign that the mounts are worn, though that can wait until I head over to Newick for the annual service.
Ah well, it's all part of the fun of owning an Alfa, and here I was thinking that because it's a MiTo it'd be cheaper to maintain - lol nope!