The Financial Industry is vast in London, nothing can prepare you for the size of it.
So the salaries you can get depend entirely in your specialty first, and your expertise second.
At the moment the Financial industry in London is suffering tremendously due to the sub-prime mortgage crisis and economic problems pertaining to the UK only.
If you have a job offer then take it, come and have a look and make up your mind.
As a reference regarding salaries have a look at the following website:
National Statistics Online .
If you provide a bit more information about what you do it may be possible to be more precise about the level of salaries currently being paid.
Good luck.