Lesbians and single women should be given the same NHS fertility treatment as heterosexual couples, doctors said today.

The British Fertility Society made the call in a series of recommendations to tackle "a wide disparity" on the social criteria used for acceptance on to an NHS programme of treatment.

Obese women should be told to lose weight before being considered for any treatment while couples with children from a previous relationship should not be excluded under the recommendations sent to the Primary Care Trusts and Local Health Boards, it said.

Dr Mark Hamilton, chairman of the BFS, said: "Continued inequality of access to treatment is unacceptable in a state-funded health service and the source of considerable distress to a great number of people with fertility problems."

The move by the BFS is likely to reopen the debate on whether the welfare of the child is best served by both a mother and a father.

The recommendation on non-heterosexual couples states: "Single women and same-sex couples should be eligible for up to six cycles of NHS funded donor insemination treatment provided assessment of the Welfare of the Child has been undertaken in line with the Human Fertilisation and Embryology Authority Code of Practice, 2004.

"After failed donor insemination treatment or in the presence of an indication for IVF allocation of cycles should be on the same basis as for heterosexual couples."

Liberal Democrat MP Evan Harris, a member of the Science and Technology Select Committee, said: "This is a welcome and progressive set of recommendations since there is no good reason to discriminate unfairly against one group of patients or another."

He said clinics should not be able to "hide behind" rules that the welfare of a child was best served by having a father in their lives.

"The Government needs to press on and change the law to end the discrimination. Its consultation on this ended nine months ago and that's a long enough gestation for these much needed reforms."

In July, health minister Caroline Flint said there was "probably not a case" for keeping "the need for a father" clause in fertility rules.

Other BSF recommendations include:

* Waiting times for treatment should be the same as for any other medical condition.

* Childless couples should have priority.

* No woman should commence NHS-funded treatment after the age of 40.

* Women who are obese must initiate a weight reduction programme and those severely overweight (defined as having a BMI of 36 or more) should not receive treatment until their weight has reduced.

* The age of would-be fathers should not be a factor in deciding eligibility for NHS treatment.

* Smoking should not be a reason for exclusion but patients who smoke should be given advice about its implications.

The advice comes after a survey of clinics, published in the journal Human Fertility, examined how guidance from the National Institute of Clinical Excellence was being implemented.

It found a wide disparity of access to treatment, with little planning on how to implement the guidance in full.

It also found unequal access to fertility treatment, poor planning to meet Government targets, and no clear criteria for who should receive NHS-funded fertility treatment.

A Department of Health spokesman said: "Primary responsibility for implementing Nice guidelines, including the rate of implementation, rests with the NHS at local level and we have made it clear that we expect these guidelines to be followed.

"Local policies should reflect local health needs and priorities, and we recognise that there are variations in IVF provision. That is why we are working with Infertility Network UK on engaging with PCTs to help ensure that fertility patients' voices are heard when decisions about service provision are made.

"Infertility UK are identifying good practice and sharing it among PCTs and, as work progresses, will discuss the extent to which the British Fertility Society recommendations have been helpful to PCTs."

The BFS said underweight women and those classed as just obese (BMI over 29) should be referred for advice from a dietician, provided with access to exercise advice and warned of the potential risks in pregnancy.

It added that NHS funding of their treatment should be deferred until they "demonstrate response to these interventions".

Richard Kennedy, of the BFS, who led the study, told the BBC: "The NHS is already stopping women who are obese from having fertility treatment.

"What we are saying is that they should be less stringent and more consistent with how they apply this.

"Obese women are less likely to get pregnant and more likely to encounter health problems. It makes sense to address obesity before seeking fertility treatment."