A superbug has closed a ward at the hospital where Prince William and Kate’s second baby is due to be born.

A surgical unit at St Mary’s Hospital, Paddington, has been shut down after eight patients were infected with potentially deadly CPE (carbapenemase producing enterobacteriaceae).

The Duchess of Cambridge is nearing her due date and is expected to return to the hospital’s exclusive Lindo Wing to give birth to the fourth in line to the throne.

But the 20-bed Zachary Cope ward, specialising in vascular surgery, has been out of action since April 15, the Sunday People can reveal.

A source said: “There is a massive deep-clean operation going on. There’s no suggestion it could spread to other units but it couldn’t be worse timing.”

Three affected patients developed symptoms and have been treated for CPE, which is a strand of the CRE superbug and resists powerful antibiotics.

CPE can be present harmlessly in the gut but if it invades the bloodstream or urine it leads to infections which can be fatal for weaker patients.

A spokeswoman for Imperial College Healthcare NHS Trust said: “A ward at St Mary’s is temporarily not taking new admissions after we found a small number of vascular patients were carrying a micro-organism in their gut.

“Unfortunately three of these patients developed localised infections. All have completely recovered.”

Hospital chiefs say they are working with Public Health England and continuing to screen patients on the eighth-floor ward.

Kate, 33, who gave birth to Prince George on the Lindo Wing in July 2013, is expected within days at one of 17 en-suite rooms at the separate unit, which is across a road from the main hospital.

Security has been stepped up with police sniffer dogs scouring the site and a police helicopter hovering above.

Well-wishers already outside include Union Jack-bedecked Terry Hutt, there for six days.