By this time, the UK auto industry was gaining a reputation for poor industrial relations, with a particularly lengthy strike leading to a three-month shut-down at the Dagenham plant at the start of the summer of 1971. This savaged availability of the Ford Cortina Mk III during its crucial first year. By the time the Ford Cortina Mk IV was introduced to UK customers, the cars inherited several Ford UK engines but were, in other respects, virtually identical to those branded in left-hand drive European markets as Ford Taunus models. Saarlouis was joined in 1976 by another new European plant in Valencia, Spain, to produce the then new Ford Fiesta concurrently with Dagenham. The same European strategy was followed by Ford's US rival General Motors, which in the 1970s, also merged the operations of its previously independent Opel and Vauxhall subsidiaries, with similar results. This decision to concurrently manufacture the same models in other European plants reduced the company’s vulnerability to further industrial disruption at Dagenham, and gave Ford a crucial advantage over strike-torn domestic rival British Leyland, which was often unable to fulfill customer orders during the all too frequent times of industrial unrest in the 1970s, and eventually ceded its long-standing UK market leadership to Ford, something from which it would never recover, but the duplication of production also made cost comparisons between the company’s various European plants increasingly stark. During the closing decade of the 20th century, UK government policy and the country’s status as a major oil producer left the UK with a currency which by several conventional criteria was significantly overvalued against the German Mark and the currencies that tracked it. This tended to exacerbate any cost penalties arising from relative inefficiencies in the Dagenham plant’s operation, and new model investment decisions during the 1990s tended to favour mainland Europe. For instance, the Sierra for the European market had its right-hand drive models made at Dagenham and the left-hand drive models in Belgium; in 1990, though, all Sierra production was concentrated in Belgium, leaving the Fiesta as the only model being built at Dagenham. The Sierra's successor, the Mondeo (launched in early 1993), was also built in Belgium. However, Dagenham did become a two-model plant again in January 1996 with the introduction of the Mazda 121 - essentially a badge-engineered Fiesta - as part of a venture with Mazda until its demise four years later. By 2000, the only Ford produced at Dagenham was the Fiesta, itself competing in an increasingly crowded market sector.