Fourteen NHS Trusts were identified yesterday with higher than expected death rates. But Barking, Havering and Redbridge was not among them – its mortality rate was better than average.

A new measure, called a Summary Hospital-level Mortality Indicator (SHMI), is intended to provide an "early trigger to probe potential problems" with the quality of care, according to the Department of Health.

But its limitation was immediately exposed by its failure to highlight the shortcomings at the Barking trust. Officials stressed it was only one indicator and could not reveal all the problems in the NHS.

The new measure monitors deaths in hospital as well as those within 30 days of discharge and is said to be more accurate.

It was developed after the scandal exposed at Mid Staffordshire NHS Trust in 2009, where between 400 and 1,200 excess deaths were not picked up.