Britain’s longest underground road tunnel could be populated with artificial palm trees, grassy verges and fake clouds to stop drivers suffering psychological problems, it has emerged.

A new study into plans for the 18-mile tunnel between Manchester and Sheffield revealed ministers are looking at unusual ways to stop drivers developing “claustrophobia, disorientation and tiredness”.

The government has named two existing tunnels – the Lærdal Tunnel in Norway and Zhongnanshan Tunnel in China – as sources of inspiration for tackling the problems.