The introduction of a 20mph speed limit on most of the borough's roads has brought some reductions in average speeds, it has been revealed.

The changes have also coincided with a reduction in air pollution, specifically levels of nitrogen dioxide (NO2), according to research by independent experts.

Richmond Borough Council has seized on the findings to argue the controversial 20mph limit has been a success.

An independent report looking at the impact of the change, carried out by air quality expert, Dr Julian Mann, of Aecom, raises questions about the contribution of the 20mph limit to reducing NO2.

The Aecom study looked at average vehicle speeds and air quality at three locations - St Margaret's Road, Twickenham; Queen's Road, Richmond, near Christ's School; and the Petersham Road, near the Rose of York Pub.

The average speed for vehicles on St Margaret's Road came down from 23.8mph to 21.8mph when comparing 2020 against 2018. The figure for Queen's Road fell from 26mph to 22.7mph and the figure for Petersham Road was down from 25.8mph to 24mph.

The study looked at NO2 levels in January to April this year versus the same period in 2020. It found there were falls, but said these are 'more likely' to have been the result of a reduction in traffic caused by the pandemic.

It suggests these reductions may have been more influenced by changes in the weather than the adoption of the 20mph limit.

Specifically, it states: "While impacts on air quality from the introduction of the 20 mph speed limits cannot be ruled out, they are likely to be minor relative to impacts from the pandemic, and difficult to identify or isolate without further study and a larger dataset."

The research suggests some of the reduction might also be explained by improvements in vehicle exhaust systems coupled with the rise of battery electric vehicles.

It adds: "Other effects, such as meteorological variability from year to year and month to month, are also likely to have played a greater role in affecting concentrations, and further effects such as the gradual improvement of the vehicle fleet through hybridisation/electrification could also have played a role."

The report concludes by saying: "The lower NO2 concentrations monitored during 2021 are more likely to have been a result of pandemic influenced reduced traffic flows."

The adoption of the 20mph speed limit on most of the borough's roads is likely to be a political hot potato at the local elections next year.

The Lib-Dem council is committed to the scheme, while the Conservatives have suggested that, if they take control, they would launch a consultation which could see it rowed back.

A council press release said: "The evidence provides encouraging early signs that lower speed limits may contribute to lower pollution levels, but this needs to be monitored further over time."

The Lib-Dem chair of the borough council's Transport and Air Quality Committee, Cllr Alexander Ehmann, said some people who argued the 20mph limit would increase air pollutant levels have been proved wrong.

He said: "When we proposed 20mph, we made clear that road safety was our primary rationale and focus. The data we've already had back, shows that average speeds in this borough reduced across the board and in some cases, we saw very large speed reductions. 20mph is working.

"We now also have independent figures around air quality and, contrary to some suggestions that 20mph would worsen the air we breathe, I am pleased with the progress and confident of the positive contribution the scheme is making to improving pollution in the borough."