Following the government's defeat over Syria in the House of Commons, former Lib Dem leader Paddy Ashdown took to the airwaves this morning. "In 50 years trying to serve my country I have never felt so depressed/ashamed. Britain's answer to the Syrian horrors? None of our business!" Oh, Paddy – what are you saying? In 40 years in politics, you'll excuse me if I tell you that I've never heard such hyperbolic nonsense. There is nothing in yesterday's decision to be ashamed of; nor should it lead either to any seismic shift in our relationship with the United States, our closest ally, or our active role in world affairs.

That a legislative assembly occasionally rejects a recommendation from the executive will come as no surprise, least of all in Washington. That's almost the norm in US politics – even when the president and the congressional majorities are from the same party. I can't number the occasions when I was told that the US administration wanted to do something, but Congress was going to get stroppy. Famously, Bill Clinton signed the Kyoto protocol, only to have his support rejected unanimously by the Senate.

On the six occasions since I entered the Commons in 1979 when it has been asked to endorse UK involvement in military action, there's been an overwhelming, bipartisan majority. What was different last night was not that MPs had suddenly decided pacifism was the answer, that we should retreat from a dangerous world; nor even that the consequences of Iraq had paralysed the capacity of parliamentarians to make decisions.

What was different was, to quote Fraser Nelson, editor of the Spectator, that "Mr Cameron lost due to the simple weakness of his case ... [H]e had no answer... Normally those advocating action offer a plan – of sorts. In Iraq, Afghanistan and Libya the plan was to replace a dictatorship with a democracy – and while you could disagree passionately, you could see what they had in mind. Not this time".

The inadequacy of the prime minister's argument was then compounded by a lamentable performance by Nick Clegg in winding up the debate. He lacks a familiarity with foreign policy, and is more likely to provoke his Conservative colleagues than ever he is to persuade. If William Hague had wound up for the government, as he should have, the vote may have gone differently.

The lack of clarity here about the plan was compounded in Washington, by two errors. First, by a timetable that seemed to have more to do with the president's travel plans – he's attending the G20 summit in St Petersburg next week – than a care for the needs of his allies. Second, by high ambiguity in the purpose of this military action.

On Thursday, the president described his plan as a "shot across the bow" of the Assad regime. Words have meaning. Shots across bows produce no damage, no casualties. It was an extraordinary metaphor to chose; a euphemism which was bound to obscure further exactly what the president had in mind.

Labour's amendment last night was designed to fill that void, to set out a process for taking a clear decision on military action, on evidence. The government could, and should, have accepted it, and Cameron would have enjoyed a brighter morning if he had.

It is condescending of Ashdown to imply that only those who voted for the Government motion believe that Syria is our business. The agony for all of us is to judge what we can do which would not further inflame the horrors in that benighted country, and which would help facilitate the elusive political solution that can be the only way to end this bloody conflict.

To achieve such a settlement we need greater engagement with both Russia and – especially given the opportunity presented by the election of the new president, Hassan Rouhani – with Iran. Diplomatic endeavours are afoot to set out a political roadmap for peace in Syria. The UK, in light of last night's vote, must redouble its efforts to be part of, and assist, such initiatives.

Britain will remain one of the closest and most reliable allies of the US, a cornerstone of the western alliance, and even now with among the most effective and active armed forces. Two years ago this same House of Commons approved our action in Libya, which the prime minister had commendably led. It will do so again – when the case is strong, and the strategy is clear.