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HJS retrofit system for London TX4 black taxis approved — but TfL age limit decision still pending

Updated: Jul 6



In a long-awaited development for London’s black cab drivers, HJS has confirmed that its retrofit emissions system for the TX4 taxi has now received official approval from Transport for London (TfL).


The announcement follows successful emissions testing carried out by UTAC at Millbrook on 30 April 2025, which provided the final piece of technical validation required.

A spokesperson for HJS hailed the decision as “the good news TX4 owners have been waiting for”, confirming that licensed operators can now proceed with retrofitting their Euro 5 TX4 taxis using the HJS system to meet stringent Euro 6 emissions standards.


However, there remains a significant caveat according to HJS. TfL has made clear that approval of the retrofit system does not in itself extend the age limit for retrofitted vehicles. Currently, even retrofitted Euro 5 taxis that meet Euro 6 standards are only eligible to remain licensed for up to 12 years, rather than the 15 years permitted for factory Euro 6 models. This contentious issue — central to the economic viability of retrofitting — is still under review.

“We have asked TfL to advise when this decision will be made,” said the HJS spokesperson, signalling growing pressure from the trade for clarity on policy timelines.


As it stands, while the retrofit approval is a welcome step forward in helping drivers comply with ULEZ and environmental regulations, the question of whether it delivers genuine long-term value remains unresolved — pending a final ruling from City Hall.


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