A maternity ward was closed for four hours after it run out of beds, it has emerged.
The closure at Queen's Hospital in Romford took place in April and was revealed at a meeting of the Barking, Havering and Redbridge University Trust (BHRUT) board yesterday.
The trust, which also runs King George Hospital in Goodmayes, said the closure was due to reaching capacity, according to Andy Walker, a member of the campaign group Save King George Hospital.
"It was confirmed in public but they refused to tell when it was closed. When I asked them why they had to shut the ward, all they said is they didn't have the capacity to cope," Mr Walker said.
The maternity ward at King George in Barley Lane closed last year as part of a reconfiguration of services, with Queens expected to take on extra patients.
However, there have been concerns over standards of care at the Queens unit and its ability to cope.
Mr Walker called for the trust to re-open the "perfectly good maternity unit" at King George to take the pressure off the Romford hospital.
He added: "Shutting the ward is a disgrace and proves the case to re-open the maternity unit.
"There is not enough capacity and we are faced with a rising population in east London and across the country."
The threatened Accident & Emergency unit at King George was given a stay of execution last month after health secretary Jeremy Hunt agreed to remove the fixed closure date of 2015.
The BHRUT has been contacted for a comment.