Mr Corbyn forced Defence Secretary Liam Fox to admit that orders worth £1 billion have already been placed for special high strength steel to build the hull of the submarines to carry the nuclear warheads.
“This is not some small project that needs a couple of parts ahead of time but the biggest of all defence items where every decision has global implications”, said Mr Corbyn.
He added: “When MPs last voted on this,Tony Blair made it clear he was seeking ‘parliamentary approval for the concept and design phase’ not the construction of new submarines. These orders are therefore illegitimate.”

