Research funded by the DfT and conducted by the independent Rail Safety and Standards Board (RSSB) found that on-train concentrations of nitrogen dioxide can reach up to 13 times higher than those next to major central London roads, with peaks occurring most frequently when trains are in tunnels or idling in stations.

While it also concluded that the air quality remains within legal workplace limits, work is under way to understand the issue and identify short-term and long-term solutions, the DfT said.

After publishing its findings, the RSSB has been commissioned to carry out a review of the regulations and standards that currently control air pollution in the rail sector. This work will include measuring air quality levels inside a further eight train classes in service across the country’s rail network.

Rail minister Chris Heaton-Harris said: “The safety of staff and passengers is our absolute priority. While these findings are within limits, I do...