Portsmouth Hospitals NHS Trust chief executive Ursula Ward has been warned that the organisation is on a hitlist of 25 acute trusts to be checked by experts from health watchdog the Healthcare Commission by the end of May.

The trust – which runs Queen Alexandra, St Mary's and Royal Haslar hospitals – has cut the recorded cases of Clostridium difficile in patients over 65 by 30 per cent from 533 to 369 in the last year.

The number of hospital-acquired MRSA infections has also dropped by more than half in three years, although the figure has not yet been revealed.

Staff have been asked to provide documents including the infection control policy and minutes of board meetings.

Inspectors will assess whether the trust is complying with the Hygiene Code, which demands all 172 trusts in England have systems to minimise the risk of superbugs.

Healthcare Commission chief executive Anna Walker said: 'If we find any trust falling short of their obligation to protect patients, we will use our powers to ensure improvements are made.'