how do I dial this UK phone number?

[Barbara]

Why the 011? What does it stands for?

Here in Europe we have to dial 00 (as in 0049 for Germany or 0044 for UK) to get an international line instead of a purely national one. In the US and in Canada it is 011 instead.
So to call a normal London number which would start with 0207...in UK you would have to dial 011 44 207...