This means that the Pensions Regulator will not be able to force Nortel before a panel hearing in the UK, as it had hoped to do, and will now be treated the same as any other creditor.
The ruling in the Delaware bankruptcy court said that the Pensions Regulator had agreed to the terms laid down in September 2009 and must therefore honour the US stay on lawsuits against Nortel while it remains in Chapter 11.
Nortel's legal team argued that separate proceedings in the UK would distract its remaining staff from dealing with other concerns that it deems more pressing.
In a statement sent to MicroScope, the Pensions Regulator said: " We are surprised by this decision. We have yet to receive the court's reasoned judgement, and will consider all the options when we do so, including the possibility of an appeal."