Could you get to Trinity Vets in Maidstone? Used to go over there regularly from Essex about a 40 minute journey from Upminster I would guess. Used a few in South Essex over the years and not found any worth going back to.
I've seen Lawton a couple of times on referrals, the guy is an absolute genius. Watching him piece everything together and make a diagnosis is like an art form. I would be very surprised if he'd see a client of another practice without a formal referral though. Glad your little one seems to have improved in any case