Thanks for all of the replies.
I can take being admonished, (doing it myself, don't worry), but low mileage, older cars have been fine for me over the last 30 years. Usually it's a window motor or blower actuator that goes....engines and gearboxes fine.
In an effort to find out whether the dealer knew about the oil consumption, I tracked down the previous, and only, owner. We had a long chat. He said he had always added half a litre every 2000 miles. He also said he wasn't particularly gentle with it, and liked the top-end kick. He didn't tell the dealer about the oil as he didn't think it was too much. A VW dealer gave him 3K for it. I guess they then passed it to the small dealer I bought it from.
I notice that the consumption isn't quite as bad when driving locally (550 miles from max stick to oil light coming on). This drops significantly on dual carriageway miles (75-80mph).
The 3 month Warranty (backed by The Stig, no less!😀), doesn't cover high oil consumption, just as it doesn't cover much else!
I'll quote the Consumer Act (thanks bigjohn), to the dealer. I guess they didn't know about the issue, but given the nature of the fault, it makes the car unfit for use. If it was a wheel bearing, suspension bush or clutch, then that's an acceptable part of buying a second hand car, but the fix for this issue is potentially the value of the car, and given that it is definitely not anymore a pint every 2000 miles, it will need addressing sooner than later.
I imagine it won't be long before a black box can tell you the car's complete history of revs, speed, cornering and braking Gs, and radio listening habits. Although, even if it does it won't stop engine designers getting it wrong sometimes.