1927 saw the introduction of the six-cylinder Alvis 14.75 and this engine became the basis for the long line of luxurious six-cylinder Alvis cars produced up to the outbreak of the Second World War.

The overtly sporting 2,511cc Speed 20 appeared in 1932 and a year later, as the SB series, was treated to a number of innovations including independent front suspension and the world's first all-synchromesh gearbox.

In 1936 a larger 3,511cc engine was introduced with seven main bearings, rather than the four of the earlier Speed 20, giving an output of 110bhp.

The clutch, flywheel and crankshaft were balanced together, which minimised vibration and two electric petrol pumps fed the three SU carburettors.

The new 3 ½ litre model initially carried saloon bodywork only, but a year later it was combined with the latest version of the Speed 20 chassis to create the Speed 25, capable of a top speed of 95mph and widely considered to be one of the finest cars of its era.

Alvis never supplied a...