Congestion Charge
From the Transport For London web site:

Congestion charging is a way of ensuring that those using valuable and congested road space make a financial contribution.

It encourages the use of other modes of transport and is also intended to ensure that, for those who have to use the roads, journey times are quicker and more reliable.

The London scheme requires drivers to pay £8.00 per day if they wish to continue driving in central London during the scheme‘s hours of operation.

Congestion Operating Hours: 7:00 am – 6:30 pm Monday to Friday, excluding Public Holidays.