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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A humid night for some with thundery downpours in places.
The 20-year-old was found fatally wounded on Roth Walk, near Finsbury Park, north London at around 3am on Saturday, Scotland Yard said.
Daniel Cowell has been jailed for five years and four months after ramming a police patrol car with a stolen transit van.