Yes I have a London bar. You can no doubt buy them online and fit it yourself or it you prefer, contact North London Locksmiths on Green Lanes (google them). Speak to Darren or Dave.
I recommend Mohammad from Alpha Security Locksmiths, 80 Turnpike Lane, genuine helpful guy, 020 8881 4400.
I have one which was fitted by the police for nothing. I do not know if they are still doing this but would be worth checking with the local community police
I got mine from North London Locksmiths near the bridge on Green Lanes. Fairly easy to fit yourself you might only need a screwdriver and a drill to make the pilot holes. Depending on the geometry of your door you might need a hacksaw to remove one or other end of the bar.
Here's a good tip when fitting one. Screw the screws in at an angle. More resistance that way.
Thanks for the tips everyone!