Ninety-one 3-car units were built by Pressed Steel at Linwood near Paisley, from 1959-1961, although they were not introduced into service until 1960. A further 19 near-identical Class 311 units were built in 1967 following the Inverclyde electrification, although these units were built by Cravens in Sheffield.

Based on the Mark 1 bodyshell design, the 303s utilised electrical gear made by Metrovick. The 303s were originally dual voltage - parts of the North Clyde Line and Cathcart Circle electrification was limited to 6.25kV (rather than the standard 25kV arrangement) due to limitations in insulation technology, although this feature was rendered redundant as 25kV was eventually standardised across the entire line. Following a series of transformer explosions, the entire stock of Class 303s had to be hastily withdrawn from service after only a few weeks' service. The old steam-operated service was temporarily reinstated whilst urgent modifications were made.

One complete unit has been saved for preservation. It is a hybrid unit consisting of the driving vehicles from set 303032 and the motor coach from 303023, which replaced 303032's own damaged motor coach. Unit 303023 was one of only four to carry the later SPT carmine/cream livery.

Unit no. DTSO MBSO BDTSO Livery Location
303023 - 61503 - SPT Carmine/Cream Bo'ness & Kinneil Railway
303032 75597 - 75632 Strathclyde PTE Orange/Black

It is intended to repaint the complete set in to Strathclyde PTE Orange & Black Livery.