Cleaners at London's Waterloo station who downed mops earlier this week will strike again today - after managers failed to resolve grievances over victimisation and pay.

Workers employed by private contractor Interserve said they had routinely been underpaid and their union reps dismissed.

They also pointed to a failure to follow agreed procedures and a shocking culture of racism in the company, with one manager opining that "Interserve should not employ black people."

The cleaners will maintain picket lines from 3.30pm through rush hour. They will also take their grievances direct to Interserve HQ in Victoria.

"These staff are doing dirty jobs in often appalling conditions and the very least that they can expect is to be treated with dignity and respect," said transport union RMT general secretary Mick Cash.