I had a quick search and read a few threads but couldnt find anything identical and don't have enough mechanical knowledge to figure it out on my own.
I'm looking at a MG ZT as a winter shed. It's on 60,000 miles and seems to be well looked after with good service record including the head gasket being replaced with the updated (MLS i think) one in November 2010 @ 49k miles. I haven't seen the paperwork yet but it cost approx £900 apparently so I'd hope it was carried out correctly. I'll check and see the liner heights were checked and if there was a head hardness test carried out.
I asked if it had any issues since with the temperature or similar symptoms. About 12 months after that it apparently suffered a scare with the temperature spiking again. The owner took it to his mechanic who stated it was vital that the coolant level was checked weekly and topped up when required due to the expansion chamber on the car being too small. The owner has since been checking it and topping up when required, which is once a month on average apparently. He says that its not had temperature issues since.
Coolant is obviously getting lost somewhere, is this likely to be through the head gasket? The temperature spike is a concern but it hasn't been repeated and it's not losing all its coolant so it suggests something like a leaking hose/connection. Am I worrying about nothing? I plan on checking under the filler cap for mayo and checking the condition of the hoses and clips ( without mucking about too much with someone elses car) anything else I should be checking in person?
Heading over to Edinburgh to see the car on sunday. The private seller has been pretty honest about things and it seems to be well looked after, particularly as it's in shed budget. Not the worlds greatest car but suits our needs and if I can get a car with a sorted K then at least I've got a spare for the elise
235/40/18 will have same circumference and are standard size on Audi VW 18's so also readily available and possible cheapeer??? Also with Syu on Oponeo, cheapest on the net I could find in the past too. Good luck and hope you enjoy your new winter hack! 
I thought about pre-worn winters but most of them would be nearly finished by time we're likely to sell it on, this way they'll either last us longer if we keep the car or be one less thing to haggle while selling it. My dad's run KW27's on his jag and BMW for a few years now and never had any problems so should cope with a mighty 120bhp front wheel drive MG!