DIET Coke and Diet Pepsi contain far more caffeine than the regular equivalents of the drinks, an investigation by The Sunday Times has found.

Laboratory tests found that Diet Coke contained 139mg of caffeine per litre, compared to just 109mg in regular Coca-Cola.

This equates to 46mg of caffeine in a normal-sized 330ml can of Diet Coke compared to 36mg in a can of regular Coca Cola.

Diet Pepsi also had more caffeine, with 135mg per litre compared to 122mg in its regular product. The tests showed that caffeine levels also fluctuated in the own-brand cola drinks produced by supermarkets.

Of the own-brand colas, the Morrisons’ version contained the most caffeine, with 124mg per litre, while Tesco’s Diet Cola contained the least at 95mg per