The M4 in the South East region starts at the Berkshire/Buckinghamshire boundary between Maidenhead and Slough and ends where it passes into Wiltshire near Swindon. The whole length of the motorway from the Maidenhead By-pass to Tormarton in Gloucestershire was designed and supervised by Sir Alexander Gibb & Partners reporting to the SERCU, but the sections outside Berkshire (from Junction 14) are included in the South Western region archive.
Work on the road, although not a motorway at the time, was started before the second world war when the Maidenhead By-pass was designed on behalf of the Ministry of Transport by Berkshire County Council. Construction was started and continued for some time after the war had started and at one stage Italian prisoners of war were employed on it but, for whatever reason, work eventually had to be stopped. The beams which had been erected for the deck of the bridge over the Great Western railway were removed and taken for use as temporary bridging material for the army.
The by-pass was redesigned as a dual 2-lane motorway after the war and it became one of the first motorways when it was opened to traffic in the Spring of 1961. Only eight years later work started on it and the Slough By-pass to widen them both to dual 3-lanes.
Although the different County Councils had prepared schemes before the war intended to relieve the existing A4 west of Maidenhead with a series of by-passes to the major towns, it was subsequently decided to abandon them and to go for a motorway to link with the Severn Bridge and South Wales. Sir Alexander Gibb & Partners were appointed to study and prepare a scheme in 1961. It is understood that the Public Inquiry for the whole length from Maidenhead to Tormarton lasted little more than a week. Construction was also accelerated (the contract period was 18 months) to meet a Ministerial promise and the road was opened to traffic in December 1971. The bridges were designed using standard precast concrete components which could be assembled to meet the varying configurations at the different locations and this must have helped to speed construction on site, although the bridges were not without their critics.