We hope they kept the receipt.

Ever bought something, only to find it doesn't work and you have to take it back to where you bought it from? Well, Groupe PSA is in a similar predicament at the moment following its purchase earlier this year of Opel and Vauxhall.

The French company bought both brands from General Motors earlier this year for £1.14 billion, but now it is asking for half of that cash back because it didn't realise how bad Vauxhall's engines were. The final sum could amount to as much as £700m.

New EU pollution limits are set to be introduced during 2020, backed by hefty penalties, and PSA feels it needs to move Opel and Vauxhall's products on to its own platforms earlier than expected in order to keep in line with the new regulations.

The rule changes are causing headaches for manufacturers as not only are they looking to combat a heavy decline in diesel car sales, they're also looking to alter their product lineups to keep in line with the new guidelines.

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Opel Insignia GSi

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The argument stems from the fact that PSA believes GM misrepresented Opel’s CO2 challenges and emissions predictions during the process of the company's sale, and it is now said to be considering legal action. Both companies have started discussions according to sources, although GM insists that no formal approach has been made.

'We are not aware of any claim submitted by PSA regarding future CO2 targets and we cannot speculate on issues that have not been raised with us,' said GM spokesperson David Caldwell, declining to elaborate on whether Opel emissions had been discussed.

'PSA undertook a robust due diligence process including their employees and many experts and lawyers,' he added. 'We provided them with substantial information.'

Opel Insignia GSi