Back in the late 1950s the 4mm OO market was principally divided up between Triang Railways (Lines Brothers) and Hornby-Dublo (Meccano). Trix had a large presence in the British market with a range generally to 3.8mm scale. The Meccano empire collasped in the early 1960s and was acquired by Lines Brothers. The original intention was to merge the two railway ranges together to form Triang-Hornby.
Incompatibilities in the production process however prevented the merger in anything other than name. The vast majority of former Hornby-Dublo range was passed to G&R Wrenn of Basildon and marketed as Triang-Wrenn.
When the Triang group itself collasped the two ranges survived as Hornby Railways (ex Triang, Triang-Hornby) and Wrenn Railways (ex Hornby-Dublo, Triang-Wrenn). G&R Wrenn Ltd ceased trading in 1992 and was sold in 1993 to Dapol.

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Two new ranges were launched in 1977 which were to have a dramatic effect on the general standard of British ready-to-run models.From General Mills (Palitoy) came Mainline Railways while Airfix Products launched the Airfix Railway System.
The very neat Fleischmann style coupling was blamed for alleged poor sales of the Airfix range while the name was said to make people think it was part of the construction kit range.
During 1980 the Airfix models were relaunched as Great Model Railways and fitted with a large Triang-Hornby style coupling.
The Airfix empire folded in 1981 and its assets were acquired by General Mills. A number of GMR items were reissued or issued new (having never entered Airfix production) under the Mainline Railways label. For its own Mainline products Palitoy had commissioned Kader Industries not only to produce them but also required them to own the actual toolings. New items now included expansion of the former GMR approach with the toolings owned by Palitoy (the Class 56 and 2P 4-4-0).
In 1985 General Mills pulled out of the toy and model industry and the Mainline Railways stock in the Palitoy warehouse was sold to Dapol, who had earlier acquired a number of GMR items from the old Airfix factory. Much confusion arose from this as whilst Dapol had acquired the toolings that had been owned by Airfix and Palitoy, the Kader owned toolings stayed in the Far East and Dapol only acquired the finished models from the Palitoy warehouse.

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Apart from acquiring various items from other former manufacturers Dapol introduced a number of new items and provided near copies of many wagons for which they did not own the toolings. They did also improve a number of the older models, before selling the vast majority of the range, excluding the construction kits and ex-Wrenn (Hornby-Dublo) toolings to Hornby in 1996. The G&R Wrenn Ltd name and most of the ex-Wrenn toolings were sold to Mordvale Limited in late 2001 who adopted the trade name G & R Wrenn Ltd.

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Replica Railways have marketed a number of items produced from the old Mainline (non-GMR) toolings which remained in Hong Kong with Kader Industries, and have released a number of new items.

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Kader, having acquired the American Bachmann brand, entered the UK market in their own right as Bachmann Branchlines , initially using the tools used for the Mainline (non-GMR) and Replica models. All Bachmann locomotives have however featured a new chassis.

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Of the other manufacturers the British Trix range passed to Lilliput, although a few items were acquired by Dapol. Lilliput folded in the early 1990s and was originally sold to Herpa. The range today is with Bachmann, who have re-released the A4 in much modified form.
Graham Farish and Jouef have ceased producing OO models; the Jouef produced EuroStar, which was marketed in the UK by Hornby, is 3.5mm HO scale. Hornby have now introduced their own 4mm OO model EuroStar. Jouef was later acquired by Lima along with Rivarossi. Lima had a strong presence in the UK OO market, particularly modern image, but ran into financial difficulties. The Lima Group was acquired by Hornby in 2005.

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In 2001 Heljan entered the UK market and have since expanded to 7mm O gauge . In 2007 Vi Trains released a OO Class 37/4 in numerous liveries and followed with the Class 37/0

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