Part 1: Bugging In
So I'm in central London, which lets face it is not the place to be when the zombie's come knocking. I'm in a flat on the 2nd floor, so the way I see it from day 1 all I need to barricade is my front door, no point trying to secure the whole building.
Beforehand I'm gonna need to pick up supplies. Fortunately I live within 200 metres of a sainsburys and tescos so, assuming I hear the news fast, I should have time to pick up some basics to last a couple of weeks before the crowds turn up. After this point i'm in a good short term situation, i'm fairly certain I can make my flat inaccessible but supplies are the problem, as once the Z's get into the area there no going outside for some time.
Part 2: Bugging Out
Getting out of the middle of the city is something I am having trouble figuring out. From where I am I can feasibly get down to the underground lines running behind the house. Not somewhere I'd really like to go but I figure it'll be less crowded than the streets, and less risky than trying to get out of my building through the front door.
From here I should be able to get out to an empty street to get a car, taking with me whatever kit I can assemble. Right now I just need to get out of the city, there is no facility to upgrade the car at all. Got a 6 lane road just round the corner that leads straight of town. I figure a wider road gives me a better chance of avoiding having to ram any obstacles. Right now though the plan is to head south.
I've got a spot in mind. Bodium Castle down near hastings about 100 miles out of town. This place is 700 years old, got a huge moat (more of a lake) and only path into the castle (which has 2 drawbridges on it too). If myself and a few others can make it this far, I think we stand a chance.

Part 3: Digging In
Upon initial arrival, securing the base is very simple, 2 drawbridges up and we've got a ready madefortress. The island between the drawbridges could be turned into a quarantine area for new arrivals. In terms of defence, I don't know of any places to acquire guns just yet so that'll certainly need some addressing, but so long as we're in the base that's not a problem, nothing's getting in. Leaving the base however poses a serious risk to those leaving, and we're gonna be needing food. This is my other main concern for the short term, so food and supplies are gonna be tricky.
Part 4: Living
In the long term the site has some major benefits.
-It's a castle, so no zombies getting in, a 2 stage entry makes sure of that.
-Surrounded by fields providing good scope for growing crops.
-Right by a river, meaning fresh water a possibility, also fishing.
Once these supplies have been established it should be possible to continue indefinitely. Hopefully being able to attract more survivors over time to a point. The size of the base offers large scope for expansion internally.
Due to it's design people can come and go from the base without jeapordising its security.
Ok so this is pretty vague and probably needs a complete rethink.
UPDATE
Ok, so after some further research into this location, some rethinking is needed. Discovered some good news and some bad.
I guess the most pressing issue is that the interior of the castle was demolished hundreds of years ago, meaning it's less of a shelter and more just a ready-made wall. This isn't too big a problem however as it gives scope for new development inside, whilst the exterior still provides the same level of security.
This open space inside can be utilised for small scale growing of food for longer term survival. Upon initial arrival tents will have to be used, or the towers can serve as accomodation, over time new shelters can be constructed along the edges whilst keeping the courtyard clear.
The external walls have been restored meaning that repairworks to the actual defences shouldn't be necessary.
On the plus side I also discovered this place has a well in the basement of one of the towers, which used to provide water for the inhabitants. This is excellent news as having a freshwater supply inside the walls reduces the need to venture out into infested lands. This could be used to create a self sustaining compound, capable of housing I'd say anywhere up to 40 people, any more and the place would be too crowded and unable to sustain that many within the walls.
In terms of defending from zombies/raiders, I've discovered one larger issue. The drawbridges I've been so enthusiastic turn out to have been replaced with a permanent wooden bridge. It would be best I expect to demolish this upon arrival, assuming a boat can be obtained. I don't think in the long run it would be too difficult to reconstruct the inner drawbridge, allowing the outer island to be used for docking, and then the second level of security to stop direct entry.
By using a boat for entry, it is less likely that mistakes will happen. Although as the moat is only 2-2.5 metres deep there is the chance of zombies just wading across, though this shouldn't be too difficult to handle. I think the best defensive strategy here will be too keep a low profile. The castle isn't close to major towns etc. so large scale attack is unlikely.
Anyway, so thats a little extra detail on the location I'd head to, feel free to join in.