Right I've got a bit further I think....!
It seems the host was trying to route through br7 randomly (an old bridge interface that I had removed all interfaces from, but apparently hadn't deleted the bridge itself?)
So having done ifconfig br7 down, it's gotten rid of that interface.
Now when I ping from terminal I get a reply saying network unreachable, rather than a host unreachable reply from the br7 address.
Presumably I need to add a route back in, in order to get everything to route through the correct interface again, which I think I've done, but still having no joy.
Attached a screenshot of my routing table. Also attached is screenshots of the br configs.
Any ideas?
Thanks