Ursula Brennan, Permanent Under Secretary of State at the MOD, said: "The assessment of the risk to HMS Westminster would have taken into account the other capabilities that we had in terms of submarines, aircraft and surveillance and so on and said 'in those circumstances, do we think that is a risk worth taking?'
"That is a judgment our operations people take on a daily basis."
But Penny Mordaunt, Conservative MP for Portsmouth North and HMS Westminster's home city, said: "I'm absolutely convinced and so are other warfare officers I've spoken to that Westminster would have been in danger.