An astonishing 250,000 refugees may have made London their home over the past 15 years, yet the capital's health authorities still lack hard evidence about their health needs and interventions that work.
Now, with legislation set to ensure that asylum seekers are dispersed more widely around the country, public health experts in the capital are doing their best to share information not just across London but throughout the NHS.
A report published this week by the Health of Londoners Project, an initiative backed by London's 16 HAs and its regional office, aims to provide what it calls 'an essential backbone for planning services'.
The project's chair, East London and the City HA public health director Dr Bobbie Jacobson, says the Immigration and Asylum Bill now going through Parliament 'takes us into uncharted territory'.
Among changes proposed, the time taken to process asylum applications should fall from an average 18 months to no more than six. But the bill will also introduce a voucher system in place of social security payments.
Dr Jacobson says: 'We do not yet have enough evidence to say what the health impacts of these changes will be.'
The Health of Londoners report contains some surprises: it shows, for example, 'surprisingly good' rates of GP registration, particularly among settled communities. But it confirms the fears of many working with refugees in general that confusion remains within the NHS about refugees' healthcare entitlements and that services are often fragmented.
The report says asylum seekers find it difficult to get access to health services and many have psychological problems adjusting to their new situation.
One survey of 34 GPs in Newham found that half had had contact in the past 18 months with an adult patient who had experienced torture. But the report challenges assumptions that physical health will be poor, since 'refugees and asylum seekers tend to be relatively young and in some sense can be seen as 'survivors''.
Taking as a starting point the lack of reliable demographic data, the research pulls together figures from a range of sources to estimate that between 240,000 and 280,000 refugees have settled in the capital since 1983 - around 85 per cent of the national figure. Of those making asylum applications, three-quarters are aged 20-39, and a similar proportion are men. During the 1990s, around 87 per cent were single people.
The research suggests that refugees are spread widely across London. But while the report warns that it is difficult to generalise, as refugees do not form a homogeneous group, some health issues are specific to refugees as a whole. Most refugees have come from poor countries which are experiencing conflict. 'Some groups may have travelled via refugee camps where there is inadequate sanitation, bringing nutritional problems and communicable disease.'
The diseases which affect refugees and asylum seekers, says the report, are in part determined by their country of origin. TB, lice infestation and gastroenteritis are common.
TB in particular remains a problem - the stigma surrounding it may lead some to reject screening, and the assumption that all refugees may be carriers can lead to discrimination.
As 'strangers in a strange land, with few if any social support networks', research shows that refugees often find it difficult to access and use health services.
And while settled communities have high rates of registration with a GP, 'there are still widespread reports of problems with first registration, and with the high proportion of cases where the HA has to allocate a GP'.
Barriers include problems with the language and culture, a lack of information about health services, and a lack of awareness among NHS practitioners.
'There are reports that some practices have asked for a passport or permanent place of residence before registration,' the report says.
Many HAs, meanwhile, continue to see local authorities as the lead agency in dealing with refugees, and it was 'not always easy or possible to identify a single lead person' in each HA.
Every HA contacted reported at least one project or programme related to refugees and asylum seekers, but most of those working on refugee health thought it should be higher on the agenda.
'Many suggested that there must be scope for joint work with particular refugee groups, numbers of whom may be small in individual HAs, but substantial across Greater London.'
But if that is to happen, argues Dr Jacobson, HAs need better information.
'Joined up government at its best will ensure that refugees coming into the UK feel welcomed and better informed about access to health and other services in future,' she says.
Refugee Health in London: key issues for public health. The Health of Londoners Project. 0171-655 6778.