The best ideas often come from lateral thinking. Wind tunnels make the air move at speed around the object being studied. The obvious, easier alternative is to make the object itself move – normally pretty easy for a powered vehicle with wheels – while keeping the air still. At a basic level, this is easily done, and much aerodynamic testing does take place in the real world. But the consistency required when chasing fractional gains has always been a challenge given the influence of prevailing wind, weather and variable temperatures. What’s needed is a carefully controlled environment – one sealed from the influence of the elements. The idea of using an existing tunnel isn’t a new one. In the US, Chip Ganassi Racing took over an abandoned one in Pennsylvania in 2003, and this has since been used extensively for motorsport development (including, reputedly, by Formula 1 teams). Here in the UK, aerodynamicist Rob Lewis had a very similar idea. Having worked for the BAR and Honda F1 teams, Lewis founded his own company, Totalsim, specialising in computational fluid dynamics (CFD) modelling. As well as automotive clients, Totalsim has worked closely with athletes seeking to improve aerodynamic performance, especially cyclists; so much so that Lewis has won an OBE for services to Olympians.

In 2013, he decided to look into the possibility of repurposing an abandoned railway tunnel in Britain for testing. And by happy coincidence, the longest, straightest and tallest of these proved to be in Catesby, four miles south-west of Daventry, so pretty much next door to ‘motorsport valley’.

“There was lots of climbing through nettles when we first came to have a look,” remembers Totalsim’s Jon Paton, the aerodynamicist who shows us around the site. “Then we got to the small matter of finding out who it belonged to and negotiating to use it.”

Once inside, they found the tunnel was partially flooded by blocked drains and the vertical vents that once carried smoke away was full of dead birds and animal bones. A collection of recovered relics now sits in the covered workshop. Protecting the habitat of the bats living within the abandoned structure required it to be narrowed at each end, so they would still have space close to the portals. Eight years later and with around £20 million spent so far, the tunnel is close to its rebirth.