I would slaughter the zombies.
shadexii has the right idea.
However, I would suggest making sure that at least one part of the multistory car park is sealed off and made accessible. A shopping centre/mall is the best place to defend from zombies in a city, so long as it has doors and several floors.
You could use guns.. sadly you can only have dual barrel shotguns here. A decent alternative would be sharp bladed weapons, if there's no guns.
Eventually, it would be wise to gather supplies and equipment from around the city, and stock them in large vehicles, fleeing to a castle(there's castles in Britain)
Then, not only would there be a fortress in which survivors could restart civilization, but the place could last indefinitely, possibly using the local area for farming, and surviving until it becomes neccessary to gather supplies from an urban area again.
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Lalalalai.... I'll cut you up!