While Whitehall and the British military fret over the impartiality of senior generals and the Americans ponder whether to send more troops, the killing continues on the ground. Also rumbling on – again in the background as far as the London media is concerned – is the question of Afghanistan's fraudulent elections. One day, decision-makers in the West will realise that this last question, the legitimacy of our country's government, is the one that will decide when the killing stops and when the troops can go home.

Since the fall of the Taliban, it has been the United Nations that has steered Afghanistan's political and economic reconstruction. While not perfect, the setting up of the post-Taliban transitional government, the Presidential election of 2004 and the Parliamentary elections in 2005, were all important milestones, for which we owe the UN thanks. But in recent months, the UN has both failed in its duty to help uphold the independence of the electoral process and lost its own claim to impartiality.

In doing so it has greatly contributed to the current crisis and has undone much of its earlier good work. I take no pleasure in saying this, and feel I have to speak out because of the gravity of the situation. I was elected as an MP for Faryab province in an election which the UN supported. I am typical of many within and outside our Parliament, from all ethnic groups, from all parts of the country, who supported and continue to support the re-establishment of democracy in Afghanistan and who have been concerned at how this has been subverted.

Despite official denials, over the last four years, the reconstruction process has been failing. For too long there has been a refusal to recognise the problems. "Things are difficult in Afghanistan," they say. "The President is well-intentioned but surrounded by Machiavellian advisers." "The Nato allies don't co-ordinate properly with one another and with the Afghans." All these excuses – in the face of a complete mess – ignored the fact that the problems were largely government-made and not inevitable. Corruption was rampant. Friends of the President were installed in official positions, often leading to abusive governance, which at worst pushed many to join the Taliban. State institutions were taken over by mafias. The Ministry of the Interior failed to reform the police, whom they have sent to their deaths in their hundreds. Reconstruction resources have been squandered. And, the counter-insurgency strategy has failed because, vitally, it lacks leadership from the government in Kabul.

These are Afghan government failings, not international ones. But none of our international partners effectively took the government to task for this – not the UN, not the US. The subordination of the international partners to the government was almost complete. The UN by this stage had largely become irrelevant.

Then came the elections. This was the opportunity for the process to be put back on track and for the people of Afghanistan, excluded by the style and substance of the Karzai approach, to reconnect with the country's political process. This was also the opportunity for the international community – the UN in particular – to redeem itself, to help ensure that the process went smoothly, and to help reverse the country's political stagnation. The outcome was immaterial – what was critical was ensuring that it was fair and transparent. This was the expectation at the popular level, though nobody expected this to be perfect or easy, and there was obviously a danger of fraud in a country where democracy is not well established. But there were safeguards to ensure fair play. The integrity of the process depended on these rules being upheld.

The UN, however, catastrophically failed to discharge its responsibility. Fraud was widespread, systematic, large-scale and very obvious. The story of the UN's response is now well known. Peter Galbraith, the UN's Deputy Special Representative, was initially prevented from raising concerns about the 1,500 "ghost" polling centres in areas thought unlikely to open due to local instability. These centres returned hundreds of thousands of votes, almost all for President Karzai.

When Galbraith then sought to have the rules followed – and exclude suspect votes – his boss, Kai Eide, following a complaint from President Karzai, intervened, alleging "interference". But this was, or should have been, the UN's mandated job, and a responsibility we Afghans expected it to discharge.

The UN essentially failed to do its job of ensuring the Electoral Commission's independence, and then compounded the offence by withholding its own extensive information on fraud while expecting Afghans to report it, despite threats to their lives. Peter Galbraith had to leave his job a fortnight ago. That says it all.

There is now only one realistic way forward. The fraud is a reality and the Independent Electoral Commission must acknowledge this – it must accept that no candidate has secured the 50 per cent of the votes necessary to win outright on the first ballot. As article 61 of the Afghan Constitution requires, there should be a second round of voting. Given that the constitutional mandate of President Karzai has now expired, a caretaker administration will be required to run the country until such a second round can be held.

The heads of the remaining pillars of the Afghan state and the United Nations at the New York level should agree on an appropriate candidate as caretaker, who should seek a vote of confidence from the Parliament. To support this the Supreme Court can be tasked with developing clear guidance on the duties and responsibilities of the caretaker administration which should, obviously, not be allowed to interfere in the electoral process. And then, after proper preparations and reforms in the electoral machinery, a transparent and fair second round should be held.

It is only in this way that we can ensure the continuity of constitutional and legitimate government in Afghanistan – the only means we or anyone has to stabilise the country. By being seen to preside over fraud, the UN is discrediting the international community's engagement in Afghanistan, undermining any democratic green shoots and encouraging extremism. Is that what British soldiers are meant to be dying for?