Shares in the two companies accused of overcharging the Ministry of Justice for its electronic tagging contracts had fallen at the end of trading today.
Shares in Serco fell about 8% while those in G4S were almost 6% lower.
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The government is encouraging motorists to think twice about buying diesel cars in a bid to improve air quality.
Atlantic frontal systems spread rain in from the northwest on both weekend days. Windy - with gales across the north and west but mild.
The band announced at a free concert on Friday that they would take over the event's Pyramid stage on Saturday June 25.