The SR built only a small number of suburban type coaches as several of the pre-grouping companies had constructed large fleets of modern coaches. However by 1934 the former London and South Western 48’ stock was reaching the end of its working life. Conscious of the need to upgrade the stock with a minimal capital outlay CME Richard Maunsell developed a plan to re-use the exisiting bodyshells, overhauled, mounted on new standard 58' steel underframes and equipped with updated fittings like electric lighting. Brake coaches received an additional 10' guards office and luggage van section at one end to lengthen the coach.
By 1934, the Southern Region recognised that the short 48’ ex-LSWR stock was in need of some major attention as it was nearing the end of its working life. Much of it was built on wooden underframes, whilst some was still gas lit and so a programme of refurbishment was proposed and undertaken under Works Order L801 of March 1934 and Works Order L852A of March 1935.
The 58’ stock to diagrams 99 and 418 were created in 1935/1936 at Lancing Works, by taking the 48’ Composite body, cutting it and fitting to a 58’ Maunsell underframe. In the case of the Brakes, a 10’ guards van was grafted to one end, these were steel panelled, which didn’t quite match the finish of the rest of the wooden panelled bodywork. The thirds (to diagram 31) differ, in that the original 48’ body was cut into two sections and mounted at each end of the underframe, with a 10’ section being inserted comprising a single compartment, with two lavatories (side by side). The defining feature of all these ‘new’ vehicles was the triangular section weatherboard that ran the length of the body, disguising the join (the 48’ body being narrower than the 58’ underframe).
Diagrams 99 and 418 comprised 5 vehicle each, these being paired and formed into 2-coach sets numbered 42-46, these being used on several south coast branchlines across Dorset and Devon.