Linklaters refused to represent Barclays plc in connection with a controversial $3 billion loan from Qatar at the height of the 2008 financial crisis amid concerns over its legality, according to papers filed with a court in London.

The claim is made in a filing by PCP Capital Partners LLP, a private equity firm that had been working with Sheikh Mansour, a member of the ruling family of Abu Dhabi. In September 2008, Barclays had been looking to raise in excess of £6.5 billion in capital and was in discussions with both PCP and Qatar Holding, then Barclays’ largest shareholder, and a subsidiary of Qatar’s sovereign wealth fund.