The Southern Railway (SR) gave the designation 5-BEL to the five-car all-Pullman electric multiple units which worked the prestigious Brighton Belle trains between London Victoria and Brighton. These units survived long enough in British Rail ownership to be allocated TOPS Class 403. Between 1933 and 1935 the units were designated 5-PUL (the 'PUL' code was then used for the 6-PUL units).

The SR electrified the London Victoria to Brighton line in the early 1930s, and full electric services commenced over the route from 1 January 1933. For the high-profile Southern Belle Pullman train three five-car units, consisting entirely of Pullman cars, were built. All 15 cars were built by Metropolitan Cammell. In June 1934 the Southern Railway renamed the Southern Belle as the Brighton Belle.

As they were Pullman cars, owned by the independent Pullman Car Company (UK), the individual carriages were numbered in its series, taking numbers 279 to 293, and the first-class cars were given women's names while the third (from June 1956, second) class cars carried less-inspiring Car No xx designations, derived from the second and third digits of the Pullman Car Company's number. However, the units together were allocated numbers in the SR series, originally taking 2051-2053, which was revised in January 1937 to 3051-3053.