Really good locksmith we used was Kane Serrvices - he's actually based in Potters Bar (so not really SE1) but was recommended to us by a neighbour and did a great job of fitting some locks on our front door. His number is 07775421688. If you want more info just ask
Depends on what you need I guess.
I bought a key safe lock-box which can be attached to your wall/door post and be opened by inserting the correct combination, (ideal if you leave your keys in the house and then go out and close the door, or for friends/family to gain access), from Worrals in Great Suffolk St.
They seemed to know what they were doing, but I have to say that when I decided to buy a second lock-box I got the exact same one on line for two thirds of the price I paid there, and the on line one included delivery in the total price.