TfW should have upgraded these old ex BR sets to comply with the requirements for Persons with Reduced Mobility by the end of 2019.
In common with many of the UK operators, this has not been done. As a result they have a dispensation to continue to operate, on the basis that it is better to have a poor train than no train.
For the class 150s, this allows continued use until the end of August 2020. You can read the dispensation here.
For the class 153s, this allows continued use until the end of Deccember 2020. You can read the dispensation here and here
The numbers of the sets are provided in the documents. TfW cannot sit back and wait for the end dates. They must make progress to upgrade the sets during 2020.