Londoners should not be encouraged to think of themselves as victims because it could exacerbate mental health problems later on, according to experts who are beginning to study the psychological impact of the bombings.

A survey of 1,000 people across the capital will begin tomorrow as researchers start to assess how citizens are coping psychologically with the after-effects of the attack.

At the same time the mental health trusts in London have joined forces to launch a 'screen and treat' programme aimed at identifying those most affected by the bombing - the people who were in the vicinity when the bombs exploded.

Psychiatrists are keen to encourage resilience because they see it as the best way of preventing future health problems. They learnt from the New York experience when excessive therapy was used. Mandatory counselling was given to all firemen and police officers in the wake of the 9/11 attack, and far from alleviating symptoms it appeared to increase problems.

Professor Simon Wessely, an expert on Gulf War syndrome and wartime stress, said: 'You have to distinguish between the people who were right there at the time of the bombings and the general public. The former group is far more likely to have individuals who will suffer post-traumatic stress disorder and who do need intensive help.

'But there is no reason for us to think that hundreds of others will be left with illness. There are dozens of studies to suggest that people are pretty resilient. The single thing that will most help them is to have family and friends to whom they can talk.'

Wessely added: 'If commuters have an upsurge in anxiety, they should be reassured that this is not a clinical disorder. It's also understandable if they are avoiding the tube and going by bike instead because people have different ways of coping. Sometimes avoidance can be helpful because it gives you an active sense of being in control.

'But if you are finding that you can't physically face getting on the tube to go to work, then that is worrying. These individuals could go to talk to their GP.'

Wessely is professor of psychiatry at the Institute of Psychiatry in London, which will carry out the telephone survey starting tomorrow, instigated by the Health Protection Agency. His unit has studied the mental health of people who went through the Blitz during the Second World War, and studies carried out at the time show that, contrary to all official expectations, the hospital beds were not filled by people with nervous breakdowns.

Mental health charities have also expressed their belief that people will deal with their anxieties through normal processes. Andrew McCulloch, head of the Mental Health Foundation, said: 'People deal with extreme situations like this in their own way. It will be entirely normal for people to find themselves dreaming about the attacks, for example. Dreaming enables humans to process their unconscious, unfinished thoughts and feelings.'

He added that some would want to talk about the attacks. 'People will find it helpful to talk to their colleagues, friends and families, in addition to laying flowers and signing books of condolence. These are very healthy ways of coping and processing what has happened, and very important ingredients to natural recovery. We have strong psychological defence mechanisms which enable us to cope.'