How could they? From an earlier, very English, post: 

Since the EU has graciously consented to Britain keeping its imperial measurements, it is only reasonable, they argue, that we should make a concession towards harmonisation. And what could be more anomalous than the fact that the British drive on the left? In nearly all other countries, not least the USA, drivers keep to the right.

The EU, as we know, likes to rotate its Chief Decision Makers. This is only right, otherwise you would always have the French in charge of wine, the Belgians in charge of beer and the Italians in charge of music, and this would be quite unfair.

Currently, decisions about transport fall to the Italians. Recognising that changing to driving on the left will be a massive upheaval for the British, Minister in Chief Garibaldo Biscottini has delivered a groundbreaking solution: piecemeal implementation.  

“It would be absurd,” said Biscottini (in Italian), “For such a change to occur all at once. We must stagger the changes. For six months all vehicles will keep to the left, except lorries, which will drive on the right. In six months’ time, buses will also drive on the right, then after another three months, all cars over 1200 cc, then all cars under 1200 cc, and finally all motor cycles. To avoid congestion, pedal cycles will keep to the left, as before. The new rules will be phased in gradually over different roads, starting with motorways for the first year, then A roads, then B roads. In all cities beginning with a B-, the direction of traffic on one way streets will be reversed. Priority will be given to traffic coming from the right, as in France, except on Tuesdays and Thursdays.”

Rather like Italy, then. I asked Mr Biscottini if he’d ever been dunked in vin santo - sorry - what would happen to unadopted roads? He didn’t know, because he isn’t British and hadn’t read his John Betjeman. Let’s have the last bit, before it gets banned for not being multicultural enough: 

By roads ‘not adopted’, by woodlanded ways,
She drove to the club in the late summer haze,
Into nine-o’clock Camberley, heavy with bells
And mushroomy, pine-woody, evergreen smells. 

Miss Joan Hunter Dunn, Miss Joan Hunter Dunn,
I can hear from the car-park the dance has begun.
Oh! Full Surrey twilight! Importunate band!
Oh! Strongly adorable tennis-girl’s hand!

Around us are Rovers and Austins afar,
Above us, the intimate roof of the car,
And here on my right is the girl of my choice,
With the tilt of her nose and the chime of her voice,

And the scent of her wrap, and the words never said,
And the ominous, ominous dancing ahead.
We sat in the car park till twenty to one

And now I’m engaged to Miss Joan Hunter Dunn.

 You can’t get much more English than this poem. “She drove…” and “here on my right” narrow it down before you even start on the Rovers and Austins and Camberley. I suppose Betjeman must have rhymed “one” with “Dunn” and said it like "won". I'm not sure anybody does nowadays.

Americans, with their "baby beside me at the wheel" and their "Burma shave" would probably assume that the girl "on my right" was a passenger, even though she drove into Camberley. Her strongly adorable tennis-girl's hand could hold the wheel, but her left hand was kept away from any funny business by the need to change gear. Heaven knows what might have happened in one of those automatics that Americans go in for.