Thanks for the replies
Being honest, I've never used a sealant and only wax occasionally, so this will be changing to be a more regular occurrence. Will have a good read of the referenced thread, thanks.
As a last resort before taking it to be looked at by a local bodyshop, I got some kettle boiled water and a J-cloth and rubbed as hard as I possibly could. Amazingly it seems to have done the trick. I was 100% sure the lacquer had been damaged as a minimum, and really thought the paint was damaged, the finish had turned really rough and even looked like it was cracked/pitted in places.
All I can think is that only the very top coat of lacquer was damaged, and I've subsequently worn this away with my vigorous rubbing! Either that, or the remains of the bird mess had dried/attached itself to the lacquer and made it look and feel like the paintwork was knackered.
Either way, I'm massively relieved the paint itself isn't damaged. When the heavens stop coming down I'll be able to have a good look, in decent light, and see if I am missing some lacquer on these spots. But from what I can see at the moment, it doesn't look noticeable...
Will be taking better precautions with regards to sealant/wax in future