Follow your marker to start for the quest item, which is a Keycard or somthing similar. Either way it is easy enough, as the marker will point you right to it.
Next make sure to find the Manhole on this map, so your going to want to scan the CCTV junction boxes to have a complete map to locate it. Make that your first agenda in each NEW area of the game, unless your pro.
*NOTE* You may not have a CCTV box close by at this point, but the manhole is in this area on the middle flight of steps. Notice it by a HOUSE logo painted on the door. Use it to "save" progress, or travel back to safe house.
See the CCTV section of this guide for EXACT locations. Use the control find key command to find it easier in this guide.
*NOTE* There will be cracked walls you can go through in this area. Best to have your flashlight out. Knowing this will help you. Thus you may be thinking you are going in circles, which I have.
The Cover Zombie
Head up the stairs from the manhole. Working your way towards the map marker. Eventually you will encounter some zombies. Of course one of them is the widley known London soldier zombie on the box cover of the game. Kill him.
Nearby will be a room with the CCTV junction box and a NEW weapon YES !
So scan the CCTV and grab the carbine. Zombies will pop out and all that. Kill them then move on.
Follow your marker to the lockpick. Yes alot of zombies I know. Once again, check weapons/enemy/faq for more information. I am getting you through the confusing stuff. In how many ways can I say kill the zombie ?
You will encounter a door with a strange bird logo on it. This is an interesting part of the story. Anyway move inside you can heal up and save your game. You will also find the lockpick nearby.
After The Lock Pick, comes another scene you may have had trouble with.
This is just like defending the safehouse. Take em down. They will go down too.
Turret ammo auto reloads if you have it in your backpack.
In survivor mode Take these guys out fast I think they can come from ALL angles EXCEPT directly behind you. So don't worry about your back in may cause you some trouble.
Lockpick the door and go through it.
This part is linear but you will lose signal with your prepper pad so no marker. It doesn't last to long though once again linear area.
When your radar or prepper pad comes back on USE it. Also be doing this often early on checking your radar. It will save your life.
Eventaully you should easily make your way to Buckingham palace exit door.