By the time of the 1933 London Passe Transport Act, Route 88 was firmly established, connecting Acton Green to Belmont, via Oxford Circus, Mitcham and Sutton. Although cut back during the Second World War, by 1950 it had become a recognised cross-London trunk route with stops at Acton Green, Oxford Circus, Vauxhall Bridge, Stockwell, Tooting Broadway, Mitcham Cricketers (Monday to Friday only), St. Helier Rose (Monday to Friday peaks and Saturdays only), Sutton and, on a Sunday, Belmont.

The main allocation of buses at this time were allocated to Merton Garage and in May 1950, RTWs were introduced on the route as part of the successful central London trials of 8' wide buses, but in November 1958 Merton lost the 88 route and the main allocation moved to Stockwell Garage, who were running RTLs. The RTM Routemasters arrived on the route from July 1966, only being superseded by RMLs in March 1975. Operating out of Stockwell Garage on route 37 until June 1966, 359 CLT (RM1359) had entered service in December 1962. After briefly being moved to storage at Thornton Heath, RM1359 was allocated to route 88 later on in June.

While allocated to Shepherds Bush Garage, on 26 April 1974 RM1359 emerged from Finchleys Woodberry Grove Garage in a very bright, Boulogne The motorway to Europe advertising scheme that promoted travel to France by Sealink and Seaspeed, being one of only four advert buses that entered service that year. Although London Transports advert buses were limited to one per route, many MPs were lobbying Parliament to ban them, but in the meantime the bus actually ended up in Boulogne on a Chiswick Works visit that took place on 29 May 1974. The Boulogne scheme was removed from RM1359 on 26 September 1974 and the bus continued in service with London Transport until July 1987, at which point it was sold on to Brakell Omnibus Sales of Cheam, eventually being exported in May 1992 to Riparo Auto SNC in Palermo, Sicily.