London has its first Muslim mayor. Or to put it more starkly, one of the senior positions in British politics is now occupied by a devout Muslim.

Few will admit it but many Christians will privately find this news uncomfortable. According to some Christians, under Khan "we can only expect an increase of Islamic segregation in London leading to increased radicalization".

Zac Goldsmith, Khan's main rival in the race for mayor, traded off that fear and branded Khan an extremist in a desperate bid to smear his campaign. It is telling that Goldsmith's campaign has been a disastrous failure.

Over this mayoral election we have witnessed, for the first time in many years, a left wing politician with a devout faith rise to power. It is hard to overestimate this achievement.

Some aspects of the left have a longstanding difficulty with people who are devoutly religious. It is an issue that extends as far back as Marx's "opiate of the masses" phrase in the 19th century.

In recent years it has been particularly difficult to be religiously devout in the Labour party, typically encapsulated in Alastair Campbell's infamous "we don't do God" interjection.

Andy Burnham, who ran to be Labour leader in 2015, started his career with an emphasis on his Catholic upbringing. That quietened has he rose up the ranks until he revealed last year he lost his faith because of the Church's "obsession with sexuality". Liz Kendall, another of last year's leadership candidates, started out as openly Christian. In 2010 she signed the Westminster declaration of faith and used to have an intern from the evangelical charity, CARE. Similarly though, as she gained prominence in the party, the public emphasis on her faith diminished.

Sadiq Khan on the other hand has been consistently open about his faith. In an interview with Christian Today he described the influence his Muslim faith has for him and how he tries to pray when he can during the day.

During the campaign Khan made it a regular habit to visit churches and often spoke of the importance faith groups play in London.

Far from being a point of concern, Khan's election is a moment of great optimism for all people of faith on the left. It signals a greater acceptance of religion. It points to a growing realisation that faith cannot and should not be excluded from politics.

For a long time individual MPs such as Stephen Timms have demonstrated the idiocy of Alastair Campbell's insistence that Labour does not do God. But that has now hit the mainstream with the election of Khan. His brazen refusal to dumb down his religion has finally put that myth to bed.

Khan's election will create an opportunity for Labour MPs who have a faith to be more open. More importantly it will also encourage those running to be Labour candidates to be honest about their religion.

With Khan's election 'faith' is no longer a dirty word on the left. And that is something that should be celebrated by people of all political stripes, and all religions.