Britain is the largest city in Britannia. Therefore, there's a lot of stuff to do. To get into the armoury on the roof, throw the lever under the crate in outer roof access passageway, near the kitchen.

Try to kill Batlin. Use the Black Sword's Death power on him. Death Bolt is the only real way to kill him, try it. Get the Cube and talk to Batlin.

Try to kill Lord British. The three ways I know of to kill him are: use the Black Sword's Death power on him. LB get's pissed off and Arcadion says something else for a change. Double click on the plaque in the courtyard when he's standing under it. Use a cannon. You can try a glass sword, I don't know if it would work. However you kill, read the will on his body, after you talk to Nell.

Cast Armageddon and talk to LB and Batlin. Then go to the Black Gate. Elizabeth, Abraham, Hook, Forskis, and another version of Batlin are dead, but will still give the same speech about the Guardian, blah, blah, blah. Neat trick, being in two places at once.