Spoke to my account manager at Leasing Options yesterday, and he rang Seat. He seemed convinced my car would be with me as originally quoted (start of November) with maybe a week or so of delay. I ordered early August with the order being confirmed at the end of August like everyone else. Apparently Seat have just introduced a new order system where they put potential build weeks months in advance, even though they will be a lot sooner.
My account manager also said he'd been told there had been no delays in actual production. I also asked about the brexit tariff, and he said BMW have already said they'll honour pre brexit prices if there is a tariff, but VW group haven't confirmed what they'll do yet, but we'd be within our rights to cancel if prices went up.
Edit: I still don't have a build week but have been advised I should have one by mid October