I don't know what the Brits did, but when I was racing in the late forties and early fifties and was too young to drive. I rode my track
bike 15 miles to the races. And back. I simply left the right side untaped. When I got to the track I loosened the lever and slipped it off the bar, unbolted the caliper\u2014front only, no one ever ever drilled the frame\u2014then I taped the bar and went racing. After the race, I reversed the procedure. Today it's easier. Several companies make clever "cross top" hinged levers that are primarily designed for
cycle cross applications for use in conjunction with the regular levers. But they work just fine alone. They attach to the top of the bar just out board of the fat part at the clamp with a hinged clamp. I just ordered pair of Cane Creek CrossTop levers from BikeIsland.com
down in Plano, Texas for only $24 per pair total, they don't charge for shipping. SOMA Fabricators makes a prettier set for more money, but they don't have any available for now anyway. Somebody at SOMA might know the history of the cross top lever, but my best guess is that they're very recent.
Redwood City, California.