I'm not sure driving the secretary of state for business around his constituency in a Japanese sports car will do wonders for his reputation. For starters, the Mazda MX-5 is so dinky that Vince Cable's knees are up to his chin. Second, I suspect the first of this column's occasional guest passengers might prefer to be seen in a British motor. "You can't make buying British compulsory for ministers," he says, then reflects. "We've got a very good car industry, though, and it would send an important message."
The MX-5 is a pert little thing, a two-seater runaround that struggles with Twickenham's speed bumps – a very different creature from Cable's Vauxhall Astra estate ("unspectacular, solid, 100,000-plus miles on the clock"). This is a special edition to mark the 2.0-litre roadster's 25th anniversary, and comes with a few frills: hand-carved art deco panel, heated leather seats, embossed headrests and a six-speaker stereo (the sound is dismal).
But it handles brilliantly, thanks to its rear-wheel drive, and is light to the touch. (The next generation MX-5, released in 2016, promises to be even lighter.) The Mazda's calling card has always been that it is fun to drive and lovely to look at, and this holds true. It has a sleek, muscular grace, and runs thrillingly low to the ground – though taller passengers such as Cable have some trouble exiting.
I'm not sure he's really the MX-5's target market. It's famously popular with female drivers, though I don't know why a classic roadster shouldn't appeal to men, too. Still, Cable approves. "I have a split personality about cars," he admits: his affection for his Astra is counterbalanced by a liking for "cars like this, fast and sporty". A high point of his cabinet career has been test-driving an Aston Martin DB9: "They let me loose on the circuit and we got up to 150mph."
As we head towards Hampton, Cable recalls the time a buffalo charged his car. It was the late 1960s, and he was working as an economic adviser to the Kenyan government. "Fortunately," he says, "it was a glancing blow rather than head-on, otherwise I would have been in serious trouble." He pauses. "Left at the mini roundabout."
As secretary of state, Cable is responsible for the British car industry, including the development of hybridisation and driverless cars. "I've had my first outing in one," he says of the latter. "It was weird, but very safe. And we want the UK to be a leader in the field." He cycles around his constituency, and commutes to Westminster by train ("not first class, and I almost invariably stand"). When he drives, it's the Friday night trek down the M3 to join his wife at her farm in the New Forest.
There is something pleasingly contradictory about Cable. He sounds like a politician when he talks about local traffic concerns, but there is a burst of spirit when conversation alights on his passions – ballroom dancing, say, or learning to drive on an abandoned airfield in Yorkshire.
We drive past the rugby stadium and hospital, then back to Cable's front door. As he unfolds himself from the seat, I think of something he said a few miles back: "When I get the chance to do something adventurous, I grab it." I think, like me, he enjoys the zippy charms of the MX-5, even if it is Japanese.
Mazda MX-5
Price £22,995
Top speed 136mph
Acceleration 0 to 62mph in 7.9 seconds
Combined fuel consumption 36.2mpg
CO2 emissions 181g/km
Eco rating 5/10
On Vince's stereo Magic and Classic FM
• Follow Laura on Twitter.
