Vehicles that are more than two metres wide or two metres high, or goods vehicles weighing more than two tonnes, have been banned from the Rotherhithe Tunnel since September 2018.
TfL is making enforcement of vital safety restrictions in the Rotherhithe Tunnel stricter to stop vehicles that are more than two metres (six foot six inches) wide or two metres high, or goods vehicles weighing more than two tonnes, from endangering other road users by entering the tunnel.
Since February, enforcement of the weight restriction has been carried out by cameras and people driving prohibited vehicles through the tunnel have been fined up to £130 per day.
To give people the chance to get used to the new restrictions, for the first two weeks, TfL sent letters to drivers caught breaking the rules rather than issuing fines. Since then, TfL has used its discretion to limit prohibited vehicles to one fine per day.
However, TfL has continued to see a number of repeat offences by prohibited vehicles.
To keep people in the tunnel safe, from 2 December, drivers of prohibited vehicles will now receive a fine for each journey through the tunnel.
TfL is also writing to vehicle rental companies to ask them to remind their customers of the safety restrictions in place at the tunnel.
Glynn Barton, TfL's Director of Network Management, said: 'Safety is our top priority and these restrictions are absolutely essential to ensure that people can continue to use the Rotherhithe Tunnel safely.
'People driving vehicles through the tunnel that do not meet the restrictions are putting both themselves and others at risk.
'I would encourage all users of the tunnel to check that their vehicle is below two metres in height and width, and that goods vehicles are less than two tonnes in weight, so that they are compliant with the new penalties.'
TfL is working on proposals to physically prevent vehicles higher than two metres entering the tunnel.
The tunnel, which was built in 1908, was not designed to cope with modern levels of traffic.
Safety is TfL's top priority and in September 2018 it carried out detailed analysis of the tunnel's ventilation system, which would be used to extract smoke and other dangerous fumes in the event of a fire.
This showed that the tunnel's ventilation system would be not be able to cope when dealing with fires involving larger and heavier vehicles.
New restrictions were therefore vital to ensure road users could continue to use the tunnel safely, whilst TfL works on plans for the tunnel's future.
By not complying with restrictions at the tunnel, drivers are putting themselves and others at risk.
TfL is due to set out its plans for the future of the Rotherhithe Tunnel this autumn as part of its annual Business Plan.
The plan will set out how TfL intends to finance the repairs necessary to secure the tunnel's long-term future as a vital road link under the Thames in east London.