In the last few days there has been much confusion surrounding the Toxicity (T) charge. Here is a clarification of the situation via a communique from TfL to the RMT
All taxis that are currently exempt from the congestion Charge are also exempt from the T-Charge. The reason that some of the results of the vehicle checker may indicate that a vehicle is subject to a charge is because the vehicle does not meet the emissions standards of T-Charge. However, on the same webpage we also state which vehicles are exempt.
For the avoidance of any doubt, all taxis that are exempt from the Congestion Charge will not be charged any additional payments for the T-Charge.