THE derailment of a 1200-tonne freight train at Burntisland in Fife which disrupted services on the main east coast line for four days, was caused by a rare track flaw, Railtrack have revealed.

However, the line operators have assured travellers that there's no need to worry and that steps have already been taken to ensure a similar problem does not occur elsewhere.

Confirmation of the problem follows an independent rail industry internal inquiry into the incident on July 8 involving a coal train bound for Longannet Power Station.

Fourteen of the 27 wagons on the train jumped the tracks shortly after 6.30am, two of them narrowly missing a fairground family's caravan home and spilling hundreds of tonnes of coal on to the popular Links Park and beach.

''A rare type of track fault caused the incident. Railtrack and its contractors have already taken steps to ensure there are no similar faults elsewhere in the network,'' Derek Holmes, Railtrack Scotland's production manager said yesterday.

Adding that the accident on one of the country's busiest lines occurred because concrete sleepers moved slightly, he said the very short, unusual track laid about 35 years ago ''had an inherent defect which has taken until now to come to light''.

Mr Holmes said ''it would not have been reasonable'' for the firm which inspects the lines for Railtrack to have spotted the defect during routine inspections.

He added: There are a small number of locations in Britain with this type of track and we have put in place a special inspection to eliminate the possibility of this happening again. No other problems have been discovered and we are confident it is all safe.''

Meanwhile, the Health and Safety Executive says its investigation is not yet complete and there are no indications yet as to whether the matter will be reported to the procurator-fiscal.

''Obviously, when our inspectors carry out their inspection, they look to see if there has been any breach of the law,'' said an official, adding: ''Once we are able to say something, we will do so.''