Funding fears and a lack of pre-let tenants are the main doubts over plans to deliver 53m square feet of new office across the capital by 2016.

A report from consultancy EC Harris confirms the City of London is the biggest market for developers with over 60% of the total area and over 50% of the number of potential projects located there.

The average size of a City project is 420,000 sq ft – nearly twice the size of those planned for the West End or Midtown.

But all areas are facing challenges which could block the development pipeline.

Richard Taylor, Head of Commercial Development at EC Harris and author of the report said: “On paper, the development pipeline for London offices shows massive potential and investment.

“However, in reality the market is very different, with a large number of these projects unlikely to be delivered as they struggle to find pre-lets and external funding.

“To stand a chance for success, projects need to differentiate and create a significant market advantage if they are to maximise their chances of completion.”