Don't just stop at agencies either.  Ask friends already working in London
to put your CV through to their HR department, browse the local newspapers,
and get online - there are some great websites now that cater for specific sectors
of the UK and European markets. Many of them also offer notification services - you
tell them the type of job you're after, and they will email the details of relevant jobs straight
to your inbox as they become available.

Some of the more well known online job search sites are:

When meeting an agent for the first time
- treat it as a job interview.  Wear appropriate clothing, and take along your current CV and
passport, as they may want to check your visa status. If you are working through a
limited company be sure to take along your Company Registration Certificate as well.

In addition to the general discussion, they may ask you to take a typing and aptitude
test. These can take a while, up to an hour, so allow plenty of time between
appointments with different agencies.

Hint: for Limited Company owners - when negotiating an hourly rate,
generally you can charge an extra 12.2% on top of the standard rate
quoted by the agents, and this would be the normal employers'
National Insurance Contribution that they would otherwise have
to pay if you were working through them directly.  You
will have to mention this however, as agencies are
not generally in the habit of giving money
away.