Genuine Londoner speaking
And it's 020 7*******

As well as the wikipedia page above, there's proof in the fact that if you're in London, and calling another London number, you can drop the 020 but you can't drop the 7 or 8.
Oh, and there's some official proof here - www.ofcom.org.uk/consumer/2009/08/phone-numbers/#video

In terms of calling Parliament, since it was mentioned above and since I've worked there, you'll find the switchboard very helpful and most importantly very human. Call them rather than the Commons Information Office line if you know the name of the person you want to contact. Their number isn't a secret:
www.parliament.uk/directories/directories31.cfm
(annexed, Fri 4 Sep 2009, 13:23, 2 replies)

You do it your way...
and I'll do it my way. This is by far the most inane argument I've ever won.
( Albert Marshmallow is a completely irredeemable cunt, Fri 4 Sep 2009, 13:25, closed)

For very small values of "won"
That is.
(Vice Admiral Sir Charles Cockbrush KCB MBE DSO, who is finding it increasingly difficult to log into b3ta.com wants to duck your aunt and kick your puppy, Fri 4 Sep 2009, 13:35, closed)

You're wrong there
If you are in an 0208 area, like me, you can phone other numbers without the 0208 and get through, which I have done.
(Bazongaloid, Fri 4 Sep 2009, 15:47, closed)

I call bullshit
Are you claiming you can make local calls by only dialling seven digits?
(Vice Admiral Sir Charles Cockbrush KCB MBE DSO, who is finding it increasingly difficult to log into b3ta.com wants to duck your aunt and kick your puppy, Fri 4 Sep 2009, 23:55, closed)