Private prisoner transport contracts are so unreliable that the government has had to fork out £3 million a year to chauffeur them around in taxis, official figures have proved.
Shadow justice secretary Sadiq Khan had questioned how much the coalition has spent on escorting prisoners between courts and prisons since 2010.
In a written parliamentary answer, Justice Minister Jeremy Wright revealed that £10m has been spent on hired transport, including taxis, since the coalition came to power.
At the peak in 2008-09 over £3.7m was spent on the transport arrangements.
In every year since at least £3m was spent on private vehicles. Last year it was more than £3.1m.
Mr Khan said: "Taxpayers will be outraged that they are stumping up millions to cart prisoners round in luxury taxis.
"The government is already paying companies to move prisoners and then taxis to do the same job.
"Why are we paying twice? The public won't believe this and prisoners can't believe their luck."
But Prison Officers' Association general secretary Steve Gillan told the Morning Star that Labour cannot wash its hands of the scandal of contracting out prisoner escorting, which was privatised by the Tories in the early '90s and continued under Labour.
He explained that because the contracts are so rigid private companies can refuse to pick up a prisoner at short notice, leaving the taxpayer footing the bill.
"All this shows the need to end the privatisation of prisoner escorting," said Mr Gillan.
"The contracts need to be tied down. This is not new, it has been going on for 20 years. What Mr Khan should be saying is we should end privatisation."
Last month the Ministry of Justice and directors at Serco asked police to investigate alleged fraudulent behaviour by members of Serco's staff in their management of a prisoner escorting and custodial services contract.
The firm is responsible for delivering a £285m prison escorting contract in London and East Anglia but has been under investigation by the ministry for some months.
The department said that detailed audit work had shown some staff recording prisoners as having been delivered ready for court when in fact they were not - a key performance measure for the contract.