Labour's shadow justice secretary Sadiq Khan has suggested that the coalition should bar G4S and Serco from bidding for future government contracts, including a tender to run the probation service.
He also called for both the police and Serious Fraud Office to investigate all of the contracts that both companies currently hold with government departments.
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A cloudy start to the day with top temperatures of 18C (64F).
Immigration levels may need to rise, David Davis has said as he refused to commit to a cap on the number of EU citizens coming to the UK.
MSPs are expected to back Nicola Sturgeon's call for a second independence referendum in a vote at Holyrood on Tuesday.