Depression affects one in 10 people a year
Some 65% of doctors say they can "rarely" offer psychological therapy to depression sufferers within two months of referral, a study suggests.
The Royal College of GPs survey of 590 UK doctors also found 15% said access to psychological services was only "usually" possible in that timeframe.
The survey is part of a campaign by mental health charity Mind calling for better access to therapies.
The government says it is working hard with the RCGP to achieve this.
Depression affects one in 10 people a year, with more than half of those experiencing more than one episode.
The National Institute for Clinical Excellence (NICE) recommends talking therapies as the best form of treatment for mild and moderate depression.
Mind's campaign is being backed by the Royal College of Psychiatrists.
It challenges all political parties to make a guarantee in their election manifestos, to offer evidence-based therapies to all those who need them within 28 days of requesting referral.
In 2007, the government earmarked £173m to boost the number of cognitive behavioural therapists available on the NHS.
The Improving Access to Psychological Therapies (IAPT) programme aims to treat 900,000 extra people in England by 2010/11, with half of them moving to recovery and 25,000 fewer on sick pay and benefits.
RCGP chairman Professor Steve Field said: "There has been substantial improvement in the last few years but there is a long way to go.
"It is essential that the current programme is completed within the next Parliament with adequate funding for training and employing extra therapists.
"If we can treat people early we can keep people in work, keep them off medication and help them get on with their lives."
Mind chief executive Paul Farmer said talking therapies could save lives, and it was crucial that people who needed help received it as quickly as possible.
"Waiting months and months for urgent treatment would not be acceptable for patients with other health problems, and it should not be acceptable for patients with depression," he said.
A Department of Health spokesperson said more than 230,000 people had already benefited from the IAPT and that almost three quarters of primary care trusts now offered this service, up from a quarter two years ago.
But in a statement it added: "There is still work to do and we will work closely with the Royal College of GPs and others to achieve this."
Opposition parties have also pledged to widen access to talking therapy treatments.
Tory shadow health minister Anne Milton said: "In the same way that physical conditions get worse when not treated, a mental health condition will also deteriorate. This must be improved.
"We will make sure that GPs have better information about the effectiveness of talking therapies."
A Lib Dem spokesman said: "We are totally committed to ensuring that people with mental health problems are given guaranteed access to the treatment that they need and we want to work with Mind and the Royal College of GPs to find out what the spending implications would be of a 28-day guarantee."
The programme director for Wellbeing at the London School of Economics, Professor Lord Layard, who is spearheading the campaign, has stressed the economic as well as the humanitarian case for investing in treatment, suggesting that successful therapy can help many people return to the workplace.
"Mental illness is perhaps the greatest single cause of misery in our country," he said.
"The least we should offer is the same standard of care we would automatically provide if they had a physical illness."