As indicated in the previous photo of the Dinky Triumph 1800 saloon (#40B), the "40" series of Dinkys -- ultimately consisting of eight British saloon (sedan) cars -- was the first completely new series introduced by Meccano after production resumed following the end of WWII. This Riley RMA or RMB (#40A) was the first of the eight to be introduced, hitting the market in 1947.
This Riley toy was produced between 1947 and 1960. In 1953-54, Meccano modified their numbering system, eliminating the alpha-numeric two-numeral-plus-letter identification (#40A in this case) and replacing it with a three-digit numeric ID (#158 in this case). The car shown in this photo was produced before that numbering change took place, since it has the identifier "40A" stamped on its baseplate.
At the time that the actual Riley RM series of automobiles was introduced at the end of WWII, the Riley group of companies -- which had been producing cars in the UK independently since the early 1900s -- was operating as a subsidiary of the Nuffield Organization, which also included the Morris and Wolseley Motor Companies. The Riley RMA was introduced in 1945, with a 1.5 L straight-4-cylinder engine; the larger RMB was introduced in 1946, with a 2.5 L straight-4. Both cars were produced until 1952, the only saloons bearing the Riley nameplate being manufactured during this period. Since the Meccano toy pictured above was introduced in 1947, it is necessarily either an RMA or RMB (although one cannot tell definitively which).