Police have launched a criminal investigation after two babies died in hospital from suspected contaminated drips.
The two babies died on June 1 and June 10 this year. At the time, Public Health England (PHE) said it was examining 19 confirmed cases and four probable cases in England. The babies were treated for septicaemia in neo-natal intensive care units across the UK.
The probe into the deaths at Guy's and St Thomas' NHS Foundation Trust will focus on the production of intravenous feeds.
A police statement said: "Officers have also been liaising with colleagues in Cambridgeshire Constabulary about a third baby who also died in similar circumstances at the Rosie Maternity Hospital, part of Cambridge University Hospitals.
"We are aware of a small number of other babies who received this feed and are working with relevant agencies to speak to those families."
Guy's and St Thomas' released a statement confirming it was one of six trusts that had been working with health watchdogs over the suspected contaminated drips.
"We are co-operating fully with the police in their investigation," said a spokesman for Cambridge's Rosie Maternity Hospital.
PHE said the cases were "strongly linked" with a number of batches of a liquid called parenteral nutrition, which was fed to the babies through intravenous drips.
The Medicines and Healthcare Products Regulatory Agency (MHRA) issued a critical Class 1 Drug Alert and recalled the contaminated liquid.
ITH Pharma, who supplied the feed, said at the time the suspected contamination has been traced to a "sourced" single raw ingredient.
One of the babies who died at St Thomas' Hospital was nine-day-old Yousef Al-Kharboush.