COSTING an estimated £16bn, Crossrail will be the biggest railway project in London since the Victorian era.

It will transform not only transport across London and the south east but the economic prospects of communities along the route.

This stretches across from Maidenhead and Heathrow in the west, through Ealing to Paddington, past Tottenham Court Road and through the East End into Newham.

It then splits into two, with one branch heading north through Stratford and into Essex and the other south through the Isle of Dogs, where it crosses under the river into Abbey Wood.

The exact route of this southern branch is what is the current bone of contention.

It first became a serious possibility in the late 1980s when it became obvious the Tube network was approaching capacity.

The Government commissioned a survey to investigate how this could be solved and in 1989 the Central London Rail Study proposed three different projects.

Work began on these but had stalled by 1994 - but not before the Government passed an order preventing development along much of the route.

In 2000, the Government revived Crossrail and the following year saw the formation of Crossrail Ltd, a 50/50 joint venture between Transport for London and the Department for Transport.

It is responsible for defining the routes and driving through the project.

Over the past six years it has arrived at the current plan.

It is hard to overestimate the transformative effects of Crossrail.

At a stroke it would allow a brand new network of services to run across London and beyond.

It would also allow suburban rail routes to run across London.

Crossrail would allow the continued growth of the capital as a primary and business centre.

But if it does not go ahead then the implications are serious.

We could see the gradual seizing up of the capital's congested transport system.

This could then see London fall away as a favoured destination for the world's businesses.