Britain stood isolated in the eyes of the world yesterday after “special relationship” ally Washington announced it will join an international conference on nuclear weapons that the Tory government is poised to boycott.

The US State Department decision to attend the Humanitarian Impact of Nuclear Weapons summit in Vienna is a major embarrassment for the Foreign Office just days after Undersecretary of State Tobias Ellwood suggested in the Commons that “the goals of the conference are unclear” and no permanent UN security council member would go.

He was left red-faced yesterday as the US stated its belief that the event — set to include over 150 countries — would see “real prospects for constructive engagement with conference participants.”

Campaign for Nuclear Disarmament general secretary Kate Hudson welcomed Washington’s stance and urged Britain to follow suit in order to prove its claim to support global steps to abolish the WMDs.

She said: “After ignoring previous invitations, countless questions in Parliament over the past year, and an early day motion signed by over 60 MPs it is high time the British government did the right thing and accepted the invitation.

“It is clear that the majority of states around the world are fed up with the faltering process of the nuclear Non-Proliferation Treaty.

“The conference in Vienna is unequivocally part of the kind of multilateral process which the UK government consistently says it supports, but when it comes to the crunch you can’t see them for dust.”

Islington Labour MP Jeremy Corbyn challenged the 

British government last week on its boycott but was batted down by Mr Ellwood.

Mr Corbyn pointed out that 128 nations attended the 2013 conference in Norway, 145 went to Mexico earlier this year and the New Zealand government, on behalf of 155 nations, have urged universal attendance at this conference.

“Britain should be there and should not boycott it,” he added.

SNP MP Angus Robertson backed his call, asking: “What message does it send to the rest of the world and to rogue regimes that seek to have nuclear weapons that the UK is prepared to boycott such a conference?”

But Mr Ellwood declared: “We do not believe that a ban on nuclear weapons is negotiable.”