and if all else fails there is always a chainsaw.
I'd... seriously suggest not using a chainsaw.
Anyhoop, my plan's updated a bit- gather weapons, supplies and friends and head to either
A. Caerphilly to hole up in the castle:
Because seriously, no fecking way zombies are getting in there. That island can even be used as an airlock/crops and livestock area. And thanks to tourism, the interior of the castle is in very good nick. Just need to uncap the well and you're in business.
or B. Barry to set up in St. Catherine's fort.
Again, incredibly defensible. There's always desalination for water if needed, plus you have coastal access for looting.