The third phase of London's Low Emission Zone initiative will be put on hold because of the financial outlay that UK firms would have incurred to ensure that all their vehicles were compliant with the new requirements.

Many small businesses in London use company vehicles, which may have required modifications to meet the new criteria.

Major Boris Johnston made the announcement today, in which he confirmed that the first two phases of the scheme - which target the most heavily polluting vehicles - would continue to run.

"Simply put, the cost of fitting pollution equipment or getting a new vehicle would have come as [a] punch in the ribs to those who need our help at this time, would have destroyed profit margins and endangered our businesses," said the major.