Even before the formal announcement of Sadiq Khan's victory in the London mayoral elections, the recriminations among his opponents in the UK Conservative Party's high command had begun. Andrew Boff, Conservative leader in the London Assembly, the elected body representing residents of the British capital, stated on television that the campaign led by Khan's opponent Zac Goldsmith had “done real damage” to relations between the Conservative Party and London Muslims. In a withering assault, he claimed that the Goldsmith campaign had attempted to “equate people of conservative religious views with sympathising with terrorism”. Boff is one of the most senior and highly regarded Conservatives in London. His views carry weight, and I know from personal conversations that they reflect the opinions of dozens of Conservative activists and MPs who have been appalled by the tone and style of Goldsmith's campaign to gain power in London. Goldsmith focussed relentlessly on negative campaigning and repeatedly targeted Khan as a Muslim, stigmatising him on account of alleged connections with so-called radicals. Goldsmith's campaign played down the issues that genuinely affect Londoners, such as housing and transport, and attacked the Labour Party candidate. Crucially, this focus on sectarian politics seems to have been led from the very top of the Conservative Party itself. In a very disturbing intervention, UK Defence Secretary Michael Fallon notoriously suggested Khan could damage London's security. Meanwhile, Prime Minister David Cameron relentlessly focussed on Sadiq Khan's alleged “extremist” connections during questions in the UK parliament. In an attempt to damage the Khan campaign, Cameron went to the outrageous lengths of claiming that Suliman Gani, an imam in Sadiq Khan's Tooting constituency, was an “IS supporter,” in a reference to the terrorist Islamic State group. Downing Street still refuses to retract this extremely damaging and false statement. London voters this week overwhelmingly rejected this brand of sectarian and divisive politics. The scale of Khan's victory was a humiliation for Goldsmith and a rebuke for his Conservative Party machine. I hope it will lead to soul-searching in the party's high command, especially because this week's results in London were far worse for the ruling Conservatives than in other parts of Britain. The Conservative Party has made progress in Scotland and held its ground across England. Only in London has it crashed to defeat. I believe that the London 2016 mayoral elections will go down in history as one of the most noxious political campaigns of modern times. It has already drawn comparisons with the notorious 1983 by-election in Bermondsey, where the Labour Party candidate Peter Tatchell was targeted. Smethwick in 1964 when the Conservatives ran a racist campaign against black immigrants to the UK is an earlier comparison. It is paradoxical that Goldsmith made his reputation as an especially fair-minded and decent MP for Richmond, a London borough. I still believe that he is at heart a decent man. But if he is to save his reputation, he needs urgently to apologise for his disgusting campaign. But we Londoners can feel proud of ourselves. Khan will be the first Muslim mayor of our great city. This is an historic moment because Khan has won the office with the biggest electorate available in British democracy. He will be the most visible politician in the country apart from the prime minister. We Londoners put him there, and ignored the rancid slurs from the Conservative camp. London, and Britain, has a great deal to celebrate. As for David Cameron's Conservatives, they have demeaned themselves. They need to reflect on their crass and ugly behaviour. We Londoners have taught Cameron a lesson in basic decency. Three cheers for us and three cheers for Sadiq Khan! The writer was British Press Awards Columnist of the Year in 2013.