It covers an area the size of five football pitches and anyone driving past the Harwell and Chilton science centres in south Oxfordshire could be mistaken for thinking a new sports stadium was going up on the site.

But the giant Diamond Light Source - described as a 'super microscope' housed in a striking doughnut-shaped building - is the largest science facility to be built in Britain for 30 years.

Construction work on the £252m project has now reached the halfway stage, and Diamond's chief executive Prof Gerhard Materlik told visiting scientists from Reading University that experimental equipment would start to be installed in October.

Permanent staff including engineers, scientists, support workers and technicians from around the world have been recruited, and more than 300 will be employed at Diamond when work is completed in 2007.

The centre, which will enable scientists to look deep into the basic structure of matter, will also be used by between 2,000 and 3,000 visiting scientists each year from around the world.

Staff are expected to move in during February.

Prof Materlik said: "Diamond will be the centre of scientific excellence for synchrotron light research - recognised as a world-class facility."