Meccano colours were changed again at the end of 1934. Plates were now blue with gold cross-hatching and Strips and Girders for the home market became gold. These latter remained green for overseas markets where many a youngster in pre-war days could not understand why the colour outfit labels and manual covers showed gold parts which in his set were very clearly green! A notable exception was the Indian market, where imported blue/gold sets and parts were evidently identical to those sold in Britain. The most significant new introductions at this time were the series of Flexible Plates and Strip Plates - at long last models could now be built to look less skeletal and more realistic. The traditional numbering of the outfits was replaced by an alphabetical series, from A to L, omitting I and J. The L Outfit was comparable to the earlier No. 7, but with the inclusion of some new parts, most notably the new flexible plates - in terms of parts content, it is often regarded as the best of the largest Meccano outfits. The Meccano Lighting Set was also introduced at this time. The Channel Segment was dropped by 1935, being, perhaps, the first significant part to be deleted permanently from the Meccano inventory - up to this time there had been mainly a steady increase in the number and diversification of parts. The vertical (1929) Meccano Steam Engine also disappeared by this time. The introduction of new parts reached its peak by 1935, and included the Helical Gears and Gear Ring after which little was added up to the outbreak of war in 1939. The non-constructional Meccano Sports Car was introduced in 1936. By this time three clockwork, and three electric motors were available. After Frank Hornby's death on September 21, 1936, his elder son Roland took over as Chairman of Meccano Ltd.

In 1937 a new set numbering system from 1 to 10 replaced the not-so-popular alphabetical series. A substantial variety of new models was also included in extensively revised Instruction Manuals. Although the largest Outfit No. 10 was significantly reduced in content from the L Set, it was nevertheless to remain substantially unchanged from its introduction until it was finally discontinued half a century later in 1992. The 6 and 20 volt "cricket ball" motors and the Hornby Dublo railway system made their appearance in 1938. In 1939, the first Meccano theme set appeared, the Mechanised Army Outfit.

The onset of war in 1939 had a progressive effect on the quality and quantity of Meccano products. The Meccano Magazine steadily reduced in size from the heady days of the mid 1930s of 100 and more pages per issue to fewer than 40 after 1941. Nevertheless the full range of Meccano sets was still available as late as 1941. From 1 January 1942, however, all Meccano production ceased, by Government decree, the factory transferring to full-time war production. From the same time, the Meccano Magazine format shrank to half size, to remain so until 1961. Remarkably, considering the heavy bombing of Liverpool, the Binns Road factory escaped bomb damage.