Researchers have found a flaw in the experiment that startled the science world last year by appearing to show particles travelling faster than light.

The glitch may have affected measurements that clocked subatomic neutrino particles breaking what Albert Einstein considered the ultimate speed barrier.

Two separate issues were identified with the GPS system that was used to time the arrival of neutrinos at an underground lab in Italy, according to James Gillies, spokesman for the European Organisation for Nuclear Research, or CERN.

One could have caused the speed to be overestimated, the other could have caused it to be underestimated, he said. "The bottom line is that we will not know until more measurements are done later this year," he added.

The results of the experiment were received with great scepticism by scientists when they were published last September because they seemed to contradict Einstein's theory that nothing can travel faster than light. That rule is fundamental to modern physics and breaking it is seen as a step into the realms of time travel.

Even researchers involved in the experiment cautioned at the time that the measurements would need to be independently verified by other scientists before a genuine finding could be declared.

The experiment involved neutrinos being fired from CERN's site on the Swiss-French border to a vast underground laboratory 454 miles (730km) away at Gran Sasso in Italy.