Old Compton Street is a vibrant street in the heart of London - the home of not only one of the biggest gay scenes in Europe, but also theatre-goers, tourists, media workers, locals and many more.
It is barely used by cars anyhow, and has an abundance of cafes and bars ALL of which would benefit from spilling out into the street, yet most of which are prevented from doing so.
There is a huge shortage of outdoor space in Soho and changing this to a shared-use street where pedestrians take priority would be a significant and valuable addition, creating a great friendly public space, bringing in a lot of money through increased capacity and usage, and making Soho a world-class destination.
Brighton accomplished this with huge success on New Rd - http://www.gehlarchitects.com/index.php?id=159503 - the same model could apply here, or an alternative could be found.
Clearly, allowing for deliveries etc. at certain times of the day is important, and easy to manage (look at virtually every pedestrian zone in the country, it's not hard!)
So come on Westminster, make Soho the amazing destination it could and should be, make an open continental-style space people can east and drink outside in and enjoy the few enough days of sunshine we have!