In message .com,
funkymonkey writes

Can someone please tell me how you actually pay for the congestion
charge? I will be visiting London soon and a friend came back from
there and says he got stung with a large fine for not paying the toll
(through his car hire company). He said he never encountered any
toll-booths or e-tag systems.

You have to pay either in advance or on the day that you travel (up to
midnight - but if you pay after 10pm there is a £2 surcharge). If you
are driving within the zone for several days, you will need to pay for
each day that the car is within the zone (even if just parked) -
although note that it operates only between 7.00a.m. and 6.30p.m.,
Monday to Friday (and not on public holidays).

You can pay on the WWW (http://www.cclondon.com/), by phone, at any of
the shops, car-parks or petrol stations that display the Congestion
Charge Paypoint sign, or in various other ways listed at the above site.

There are no toll booths, tickets or tags - the number plates of all
cars in the congestion zone are photographed automatically and then
compared at the end of the day with the list of those who've paid.

Driving and parking in central London is neither cheap nor easy (even
for those like me who have lived here for more than 50 years). Given
that the capital has excellent public transport, it is well worth
considering whether you really need a car for days spent in the central
area.
--
Paul Terry