The number of Britons prescribed antidepressants is at a record high, despite official warnings that many patients may not need them.

More than 31 million prescriptions were written by doctors for antidepressant drugs last year, figures published today reveal, with the use of drugs such as Seroxat and Prozac increasing by 10 per cent. The findings, which show a big increase on previous years, come despite growing concerns over the country's excessive reliance on chemical treatments and over their possible side-effects.

The exact number of people taking pills for depression is not known but is thought to be several million, with many taking the medications over long periods on repeat prescriptions.

The most common drugs, known as Selective Serotonin Reuptake Inhibitors (SSRIs) - which include Seroxat and Prozac - are the easiest treatment to prescribe and are often effective. However, guidelines from the National Institute for Health and Clinical Excellence (NICE) in 2004 recommended that they should not be used as a first-stop remedy for depression. They have also been found occasionally to trigger suicidal thoughts and self-harm in children and adults, and are not recommended for use by under18s.

Research on doctors' habits also revealed that many felt they were prescribing the drugs too often, but did so because patients wanted medication. They said that funding was often not sufficient for alternative behavioural therapies and other counselling treatments, despite NICE guidance that they can be as effective as antidepressants for those with mild to moderate depression.

The 31 million prescriptions for all antidepressants represented a 6 per cent rise last year, while SSRI use increased from from 14.7 million in 2005 to 16.2 million in 2006. The cost to the NHS of antidepressants was £291.5 million last year, with SSRI use reaching £119.6 million.

Depression is estimated to affect as many as one in five people at some point during their lives. At any moment, 1.5 million people aged between 16 and 75 are suffering from depression, and 2.7 million from anxiety, although although most cases are untreated. Depression is responsible for 70 per cent of recorded suicides in Britain.

Campaigners also claim that taking regular exercise in a green space could alleviate the symptoms of sufferers. But a lack of funding for such treatments contributes to the increasing use of antidepressants as a "quick fix", despite government pledges to bring an end to the "Prozac nation".

According to Mind, the leading mental health charity, adult patients with moderate depression should instead be given counselling and cognitive behavioural therapy or encouraged to take more exercise.

An estimated 93 per cent of GPs continued to prescribe the drugs because a lack of alternatives, the charity said. The figures were released quietly last month, but are quoted in a report released today by Mind.

Paul Farmer, chief executive of Mind, said: "Doctors are guilty of a knee-jerk reaction in prescribing pills, which are commonly long-term prescriptions and have well-known issues with side-effects. The mindset of GPs will have to change so that they consider counselling and other forms of therapy as a frontline treatment."

But William Bird, a family doctor from Reading, said that patients increasingly expected to be given medication rather than other therapies. "Antidepressants seem to have lost the stigma they once had and now most patients seem to want to take them.

"On the other hand, it can be hard to motivate patients with depression and we need to do more to raise awareness of counselling services and promote physical activity."

David Healy, a professor of psychological medicine at Cardiff University and a leading critic of SSRIs, said that while the drugs were of benefit to patients with severe depression, the risks outweighed the benefits in those with less serious problems.