The Large Hadron Collider (LHC), the world's most powerful atom-smasher, which broke down just days after it was switched on, will not start its experiments until the middle of next year.

Officials at CERN, the European particle physics laboratory near Geneva, announced today that repairs to the £4 billion “Big Bang machine” are unlikely to be completed until late May or early June.

CERN also estimated that the bill for fixing the damage caused by a major helium leak would reach about £14 million.

The LHC was shut down on September 19, only nine days after beams of particles were first fired around its 17-mile (27km) ring, when a faulty electrical connection between two super-conducting magnets caused the release of super-cooled helium.

The fault affected a part of the accelerator that is kept chilled to within 1.9C of absolute zero (-459F), which had to be warmed up to room temperature before it could be examined and repaired.

It was initially thought that the repair process would take until the spring, encompassing a mandatory maintenance shutdown over the winter period. It now appears more likely that it will be early summer before the LHC starts smashing atoms, to re-create conditions that last existed immediately after the Big Bang more than 13 billion years ago.

James Gillies, CERN's director of communications, said: “If we can do it sooner, all well and good. But I think we can do it realistically early summer.

“There is still a lot of work to do and we want to be sure that everything is in order before starting up. We will start up the LHC again as soon as possible."

A full assessment of progress will be made when CERN's governing council meets on December 12.

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