Ford and GM's dominance in the UK can be explained by their long history in the country. GM bought Vauxhall in 1925, while Ford started making cars there in 1911. Despite Ford quitting its carmaking operations there in 2002, it has continued to hold its top spot over Vauxhall, which makes the Astra compact for it and sister brand Opel at GM's factory in Ellesmere Port in northwest England.
The problem for both brands is working out how to keep sales buoyant without dumping cheap cars on the market. That dilemma put Vauxhall managing director Tim Tozer at loggerheads with his bosses in Europe and ultimately caused him to resign, said a source close to Tozer.
"They wanted him to chase targets he didn't want to chase, and go into channels he didn't think Vauxhall should be in," the source said. "They were hellbent on being profitable in Europe."
Before resigning, Tozer had said that the UK was a profitable market. In the last two years the pound has strengthened against the euro, the currency used by the countries that build the bulk of Ford and Vauxhall/Opel cars for Europe. That increased margins and sales as customers took advantage of U.S-inspired finance schemes that kept payments affordable through low interest rates.
Also important in keeping monthly finance payments low are good residuals, but Tozer feared values would be eroded if Vauxhall started pumping more cars into low-margin channels such as daily rental fleets, the source said.
A Vauxhall spokesman denied the company was hurting the bottom line.
"We're not going back to pile 'em high and sell 'em cheap," he said. "We'll be nudging Ford quite hard next year."
Still, Tozer may have had a point.
"They need to make the numbers in Europe but it sounds like they're prepared to sacrifice long-term profit for the short-term gain," said Ian Fletcher, an IHS Automotive analyst in London, adding that factory overcapacity may be partly to blame.
"GM should have made far more of the cuts Ford did instead of having to fill those plants any way they can," he said.
A Ford UK spokesman said it had a policy of reducing its exposure to low-value business such as daily rental fleets. He said that retail numbers for 2015 through November accounted for 45 percent of sales, close to the market average of 44 percent for the same period.
The figures were boosted by the Fiesta subcompact, the UK's best-selling car, which took a 6.6 percent share of the retail market in the same period, the company said. Vauxhall didn't disclose its numbers, but has traditionally sold a much greater proportion to fleets.
The Ford spokesman denied its policy would reduce sales, but IHS predicts that the brand will have a drop in UK volume over the next few years, falling from an estimated 336,000 in 2015 to 280,000 by 2018. That would bring it much closer to Vauxhall, which IHS predicts will remain flat from the 264,000 it predicts the brand will do this year.