Work on the 80,000-seater stadium was due to begin in August but the date was moved forward, and the first steps in digging the foundations begin today.

The Olympic Delivery Authority said it had been able to make an early start because of progress already made on site.

After the Games, the £500 million stadium will be turned into a 25,000 seat venue.

The milestone comes as members of the International Olympic Committee's Co-ordination Commission enter the last day of their three-day visit to London.

The 18-strong group has been treated to a series of presentations from London 2012 chairman Lord Coe and Olympic Delivery Authority chairman John Armitt, as well as meeting Olympics minister Tessa Jowell and the new Culture Secretary Andy Burnham.

Organisers are expected to say their preparations are on track, and will be hoping to gain praise similar to that of the previous inspection 11 months ago. Work on the 2012 Aquatics Centre is due to start this summer.

Preparation for the Olympics has been marred by reports that the cost of staging the Games has soared by £5 billion since initial estimates were made.

Last month a group of MPs branded the original 2012 estimates "entirely unrealistic" and accused ministers of succumbing to "wishful thinking".

The Commons public accounts committee also said it had little confidence the current estimate of more than £9 billion would not be exceeded.