Blimey Quentin, that's rather unfortunate.
As for making a claim with Shannon's: I had to do that a few years ago when some thoughtful person left a shopping trolley behind my vehicle in a Woolworths car park. My vehicle being a van, the trolley was obscured from view as I approached from the front, hopped in the driver's door and deposited my bag of groceries on the passenger seat. Unfortunately I'd only bought a couple of items. If I'd bought several bags of groceries I would have gone around to load them in the back door of the van and found the trolley. From the driver's seat, the trolley was below the line of sight through the rear window and it wasn't visible in the side mirrors either, so I didn't see it when I checked behind before reversing out of my parking spot.
As I backed out of the parking spot, I heard a clunk and rattling noise as I gave the trolley enough of a nudge to send it off down a slope in the car park. The bloody thing gathered speed down the hill at an alarming rate, bounced off the side of a car that was entering the supermarket car park, then shot out across the road and into a service station where it hit another car before coming to rest against the kerb where the bowsers were. The first car suffered deep gouges on its side (across both door panels) and the other car was dented and scratched near the rear wheel arch. The driver who was entering the supermarket car park had witnessed the whole sequence of events and held me responsible. Fair enough, it was me who set the trolley in motion. As I couldn't point the finger at whoever parked the trolley against my rear bumper, I had to cop it on the chin. It happened just after school got out so I strongly suspect it might have been kids who set it up deliberately and were probably sitting in mum's car pissing themselves laughing at the whole performance.
I called Shannon's to make a claim. I thought it might be an issue that it wasn't actually my car that did the damage, but an intermediate shopping trolley that was shunted between my car and the others. As far as I'm aware, shopping trolleys don't carry third party motor vehicle insurance. But it wasn't a hassle at all. Shannon's accepted the claim no problem, and paid for the repair of both vehicles.
The claim process was dead easy and took about 5 minutes. I phoned Shannon's while still at the scene. I didn't know my policy number but that wasn't a problem. I was able to give them sufficient ID info for them to verify who I was. The painful bit was giving them my credit card details to pay the $500 excess. The other drivers were there as I made the call so I was able to relay their names, contact details and vehicle rego numbers. The Shannon's rep asked me for a brief description of the damage to their vehicles. I offered to take photos but he said it wasn't necessary. The description was sufficient, presumably to avoid the owners claiming other damage than I hadn't done. So I left it to Shannon's to sort it all out and finished the call. A few minutes later I received a follow-up email on my phone with the claim details from Shannon's. My entire involvement in the claim process was completed before I got home with my groceries. I presume the other drivers were satisfied because I never heard from them afterwards. I have no idea how much the repairs cost, but 2 cars with nasty dings and scratches would well and truly exceed my $500 excess.