The Rail Maritime and Transport union (RMT) said lives were being put at risk by using "inadequately-trained managers" to operate the trains.

Heathrow Express said a normal service was running and fully-qualified driver managers were driving trains "as part of their normal duties".

Up to 80 workers voted 12-1 to walk out on Thursday and Monday.

24-hour walkouts

Heathrow Express, which runs the Paddington to Heathrow Airport service, said only a few of the 275 workforce had failed to report for duties.

Station staff and other staff, including a few drivers, are taking part in two 24-hour periods of industrial action.

RMT general secretary Bob Crow, said: "Our members are out solidly today and if the company keeps their head buried in the sand they will be out solidly on Monday.

"Using inadequately-trained managers to run the trains will not solve this dispute but it will put lives at risk."

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Heathrow Express strike steams on

This is local London: 21 Septembe, 2006
By Ruth Holmes

Strikes which threaten to disrupt the Heathrow Express have gone ahead today and are set to continue on Monday.

The Heathrow Express runs from Paddington to Heathrow every 15 minutes

Nearly 80 members of the rail union RMT are refusing to work after voting 12 to 1 against a three-year pay and conditions offer.

RMT general secretary Bob Crow said: "RMT members at Heathrow Express are out solidly today and if the company keeps its head buried in the sand they will be out solidly again on Monday.

"Using inadequately trained managers to run trains will not settle this dispute but it will put people's lives at risk."

Heathrow Express managing director Brian Raven said he was confident the service, which runs every 15 minutes from Paddington to Heathrow, would continue as normal.

The company said they were "disappointed" that workers were pressing ahead with the strikes.

Earlier this month, members of another transport union, ASLEF, accepted the pay offer and called off their planned strikes.

RMT general secretary Bob Crow said the latest offer was little more than a "rehashed" version of the three-year offer the union had already rejected.

RMT has also announced that London's transport workers could go on strike in a row over pensions.

The union is pressuring Transport for London to oppose changes which they said would see people who leave work through ill health deprived of a pension.