The failure, the third in eight days, left 400 passengers, including Sir Bob Reid, the chairman of British Rail, and Sir Alastair Morton, the joint chairman of Eurotunnel, stuck on the train at Calais station for two hours.
Passengers were eventually transferred to a replacement train and reached Paris two- and-a-half hours late. Last night engineers were investigating the mechanical failure which halted the train.
On Thursday another of Eurostar's trains, which was due to take 400 journalists to Paris, failed to leave Waterloo station because of a 'technical fault' - the vacuum circuit breaker malfunctioned. The journalists left an hour late.
Last Friday, a Eurostar train on a Paris-London test run broke down near Ashford in Kent because 'a number of systems failed simultaneously' - causing delays of up to 90 minutes to services.
A spokesman for European Passenger Serices, the UK arm of Eurostar, which will run the passenger-only services from London to Paris and Brussels from 14 November, said: 'There was a problem and it was decided to stop at Calais.'
He said the company was confident that it will offer a reliable service when it opens next month.
Sir Alastair put a brave face on the incident. 'There was a breakdown due to a mechanical teething problem,' he said, but 'they were astonishingly efficient in bringing up a reserve train to Calais. We had no other problems for the rest of the journey.
'I am very sympathetic to people with teething problems and Eurostar handled the situation very efficiently.'
Railtrack has launched an inquiry into how a busy commuter train was wrongly routed on to a line already occupied by another oncoming train on Thursday night.
The incident happened near Tunbridge Wells just a few miles from the scene of last weekend's fatal rail crash at Cowden in Kent.