A day-long test of speed and reliability for standard-equipment production sports cars, the Grand Prix d’Endurance organised by the Automobile Club de l’Ouest was not the first 24-hour car race – Columbus in Ohio hosted one as early as 1905 – but swiftly it became the benchmark, due mainly to ‘Bentley Boys’ who raced even harder than they partied.

The British invasion of what was to become France’s most famous race had a rapid start: China-born Canadian John Duff was the first to enter (much against W.O. Bentley’s better judgment) the inaugural edition of 1923 and, co-driven by Bentley’s only pro, Frank Clement, won in 1924. Local resistance, however, was strong in speed and number. Initially. Chenard et Walcker scored a 1-2 in 1923 and Lorraine-Dietrich registered consecutive wins from 1925. The former claimed the Triennial and Biennial cups of 1925 and the latter finished 1-2-3 on distance in 1926. Yet both then faded into racing obscurity.

These were trying financial times for myriad small-volume manufacturers, with mergers and takeovers abounding as bankruptcies beckoned. Bentley likely would have folded, too, but for diamond heir Woolf Barnato’s regular injections of cash. British names Alvis, Aston Martin and Lagonda joined Bentley and American makes Chrysler and Stutz, plus Itala of Italy – to outnumber the French by 1928.

Le Mans was receiving widespread interest in part because of its pile-up of the previous year, at the notorious blind corner of Maison Blanche which eliminated several contenders, including the leading Bentley and chasing sister car. The team’s remaining entry survived repairs by drivers-under-instruction using only tools and spares carried in the car. Yet it won by 20 laps – a record 215 miles – after the late failure of a leader under increasing pressure. Victors Dudley Benjafield and Sammy Davis were lauded national heroes: the best of British.

Except that they hadn’t won. Not until 1928 was the car covering the greatest distance officially honoured. The original idea had been to declare victory after three years based on a rolling aggregate within capacity classes. Deemed too convoluted – and awarded only once – it was replaced from 1924 by a two-year competition. Further complexity and confusion arrived in 1926 in the form of the Index of Performance: basically, distance covered divided by target set according to engine size. It was clear by 1929, however, where the main interest lay – for the foreigners at least: Bentley dominated, Barnato putting his talent where his money was with a second straight win, this time at the head of a marque 1-2-3-4.

The foundations were in place. The Circuit de la Sarthe’s surface was by 1928 sealed throughout – mud and ruts or dust depending on the weather having been unwelcome factors – and in 1929 a short linking section constructed at residents’ behest undercut the hairpin in Pontlieue. Pits and grandstands – at their current site after a year starting/finishing on the Mulsanne Straight owing to a dispute with landowners – plus cafés, a boxing ring (!), chapel, car park and toilet facilities had also been built. And by the end of the decade those run-and-jump starts had become famous the world over.