Britain has definitively ruled out any involvement in military strikes against Syria even if further, more serious chemical weapons attacks take place, William Hague and George Osborne have said.

In his first major interview since the government's defeat in the Commons on Thursday night, Hague, the foreign secretary, said parliament had spoken and Britain would only offer diplomatic support to its allies.

He said he could only envisage a change if Labour became "less partisan". His remarks were echoed by Osborne, the chancellor, who told BBC1's Andrew Marr Show that Ed Miliband looked less like a future prime minister after helping to defeat the government.

In an interview with the Murnaghan Show on Sky News, Hague said: "Parliament has spoken. I don't think it is realistic to think that we can go back to parliament every week with the same question having received no for an answer.

"Anybody looking objectively at this would see that, in order for parliament in any circumstances to come to a different conclusion, people would have to be more persuaded by the evidence. There is a great deal of evidence there but I'm not sure that the extra evidence that the United States presented would have made a difference to those doubting the evidence in the House of Commons.

"The Labour leadership would have to play a less partisan and less opportunistic role and be prepared to take yes for an answer in terms of the motions that we present to the House of Commons. We had taken on board all the points that they had made before the debate on Thursday. All those things would have to happen to get a different result in the House of Commons and I can't see any immediate possibility of that."

Osborne made similar remarks 90 minutes earlier on the Andrew Marr Show. He said: "Parliament has spoken. The Labour party has played this opportunistically. The Conservative MPs and the Liberal Democrats who could not support us – they have a deep scepticism about military involvement. I don't think another UN report, or whatever, would make the difference. Of course I wanted us to be part of a potential military response. Now that is just not going to be open to us."

Osborne, a strong Atlanticist who has backed military intervention over the past decade, said he would make the case for Britain to remain a key player.

He said: "I hope it isn't a great historical moment. I hope that people like myself and many others who want Britain to be an outward-looking, open nation that is confident about shaping the world around it are going to go out there and win this argument."

But the chancellor was highly critical of the Labour leader. He said: "The Labour party would have voted against regardless because they played this in quite an opportunistic way. I think Ed Miliband looks a bit less like a prime minister even than he did a few weeks ago."

Ministers who feared that Britain risked isolation after MPs ruled out any British involvement in military strikes against Syria are noticeably more relaxed after Barack Obama cited the vote as he announced he would consult Congress before taking any action.

Hague said: "We were saying in our parliament that there would be a second vote at a later stage if we wanted to go ahead with military action. So that, of course, would have been rather similar to President Obama setting out this timetable in Congress now. The United States of course must make its own decision so we entirely respect and support what the president announced."

Douglas Alexander, the shadow foreign secretary, agreed that Britain would not join any military action. He told the Andrew Marr Show: "The conditions we set down on Thursday apply on Sunday morning. But since then, of course, the prime minister has given his word to the British people that the UK will not participate in military action in Syria."