Twenty airlines are served by Swissport UK from Heathrow

The Transport and General Workers' Union (T&G) announced the second walk-out on Tuesday, hours after a two-day strike ended at the west London airport.

It claims many staff working for Swissport UK have had no pay rise for 18 months and the company is accused of walking out of negotiations last week.

But Swissport, which runs baggage handling, check-in and other services for 20 airlines at Heathrow, says it faces severe problems.

The company said pay had risen between 9.5% and 17.5% over the past two years and the union's demands were "totally unrealistic".

Workers 'still angry'

Announcing the new strike, the union said its members were still angry and determined to get a decent pay rise.

National officer Brendan Gold warned that picket lines would be manned at Heathrow unless the dispute was settled.

He added he was aware of difficulties facing the airline industry, but said business was still growing.

Hundreds of staff returned to work at 0430 GMT on Tuesday after their first 48-hour walkout.

There was no sign of long delays or queues at Heathrow, but there were conflicting reports about the strike's overall effect.

The T&G said there had been "significant disruption" to flights, which had to be diverted to other airports, and that Swissport's cargo operations were badly affected.

But a Heathrow spokesman said airlines had been able to warn passengers in advance, only five flights had been cancelled and the effect was minimal.