Unite has exposed gaping holes in the state of primary care trusts (PCTs) in London, which are facing a severe shortage of staff.
In its September issue, Unite's journal Community Practitioner reported that the situation had worsened in London, with the drastic decline in the number of new health visitor registrations in the country - the number fell from 712 in 2005 to 253 in 2008.
The report has an areas-wise analysis of the problems faced by the PCTs in the capital.
According to the study, London's PCTs face problems with regard to shortage of qualified health visitors, meaning staff can feel demoralised due to being overburdened. This in turn prevents timely attention to patients, especially new babies.
Poor recruitment drives and lack of trained staff have also contributed to the problem.
Unite professional officer, Dave Munday, told Community Practitioner: "Health visiting is at crisis point - managers are training less, and 20% of the workforce could retire tomorrow and trusts cannot recruit."
He said that the crisis arose because trusts ignored warnings issued three years ago to "concentrate on investing in health visitor training".
Calling for "urgent action" to remedy the situation, he said: "Every single training place must be filled by September (2009) to benefit in the long-term."