The UK’s Pensions Regulator is planning to formally serve a demand for £2.1bn (€2.5bn) against the bankrupt Canadian telecoms group Nortel Networks, to meet the bill for its underfunded British pension scheme – just months after the US and Canadian courts both ruled out claims from the pension trustees.

The step is the latest manoeuvre in a transatlantic legal tussle that has been going on since January 2009, when the company was put into administration leaving a £2.1bn pensions deficit in the UK.