In the UK, the rules are clear: if you don't want to get pregnant, contraception should be available free of charge. Other factors may stop some women and girls using it, but the basic provision is there. Elsewhere, the picture is very different. More than 200 million women worldwide want to use contraceptives but simply cannot access them.

The consequences are stark: each year there are 75m unintended pregnancies in developing countries. That exposes more women and girls to the associated risks in a world where more than a third of a million die in pregnancy or childbirth annually – the number one killer of 15- to 19-year-olds.

And having babies when they are still children themselves – nearly 13 million adolescents do so each year – means girls have to drop out of school, missing out on the education that would give them the opportunity to escape poverty.

A high-profile summit in London Wednesday, co-hosted by the Department for International Development and the Bill & Melinda Gates Foundation, will use the message that family planning saves lives to seek donor pledges large enough to give 120 million more women access to contraceptives by 2020. But what else is necessary alongside that all-important funding? Where is change needed most urgently and how can it be achieved? And what are the potential pitfalls?

These were some of the questions discussed at a recent roundtable debate hosted by the Guardian, in association with the International Planned Parenthood Federation (IPPF). There was widespread agreement around the table that while increasing the physical supply of contraceptives to women in the developing world was crucial, it had to go hand-in-hand with better education about sex and relationships and a focus on rights. Family planning – an unfortunate, old-fashioned term, some said – has long suffered from being associated by critics with population control. Here, it was thought, was a chance to break free from that and gain real momentum.

Greater prosperity

"Now is the time not to be deterred by such counter arguments," the international development minister, Stephen O'Brien, said. Greater prosperity might be an outcome – because having fewer children and having them older means women are able to stay in education or work while investing more in each child – but it was not the driver.

"Access to contraception is just one part of an overall set of needs but we think it's an important way in, to try to put family planning back on the global agenda in a way it's lagged over the last two decades," said Joe Cerrell, director of the Bill & Melinda Gates Foundation's Europe office. "It's been incredibly frustrating to see how it hasn't risen to the extent that it needs to … It's been bogged in controversy … endless debates that don't lead to improvements … We're very, very optimistic [this] will be a pivotal moment to really change the tide."

One important shift needed was an extension of family planning services to reach unmarried women, who are too often excluded in countries where sex before marriage is taboo, the table heard. "Once you are married, you have so much more access to both information and services," said Yasmin Ahmed, Marie Stopes International's vice-president and senior regional director for South Asia, Arab world and eastern Europe.

And good-quality sex education was far broader than simply letting young people know where to get contraception, said Anna Martinez, co-ordinator of the Sex Education Forum.

Abstinence-only education presented another challenge, said Roger Ingham, professor of health and community psychology at the University of Southampton. "We do have to face up to this and look for cultural change as well as more financial input," he said.

Some insight into the attitudes faced by campaigers was given by Tonte Ibraye, the national co-ordinator of White Ribbon Alliance Nigeria, who told of a man who was advised by a friend that having sex with a girl would make a sexually transmitted infection "go away".

Ibraye, 26, one of three young people at the roundtable, also spoke of meeting a politician who described family planning as "white man's culture", telling him: "I need to have as many children as I want because, maybe, if I have 100 children only five of them will survive; maybe out of 10 children only the ninth one will be intelligent."

Concerns were raised by some at the table over whether abortion would be discussed at the summit. About 22 million girls and women will have unsafe abortions every year. In the lead-up to the summit, some people had been "trying to put the issues of family planning together with abortion … in some cases in a very unhelpful way," Cerrell said.

That discussion led participants to highlight the position in Northern Ireland, where, despite being UK taxpayers, women cannot have an abortion and must pay to do so even if they travel to the British mainland. "It's always a bit strange when we read DfID's policies about developing countries and access to abortion services, and yet we have the UK government that refuses to say anything about access to abortion services in Northern Ireland, except in a negative way," said Audrey Simpson, the FPA's director in Northern Ireland.

This, along with criticisms of sex and relationship education in the UK, which ministers have refused to make statutory, could make discussing family planning policies with other countries difficult, the table heard. There was a risk developing nations might look at this situation and say "the UK doesn't get this right so why should we take leadership from them on social and cultural change?", argued Simon Blake, Brook's chief executive.

Contributors also stressed that those delivering improved services and education needed to target all groups – male as well as female. "If you look at the language around the summit, there is so little about men and boys," Ahmed said. Yet their sexual behaviour was probably more risky than that of girls and, just like parents, community leaders and teachers, they were also "gatekeepers" who could form barriers to improved sexual health.

Nor should very young girls who get pregnant be written off as a "lost cause", the roundtable heard, when focused work could stop them having any more children while they were still too young. "They seem a little bit off the agenda," said Doortje Braeken, the IPPF's senior adviser on adolescents and youth. "Young pregnant girls have the same aspirations as others."

A key theme was the complexity of differing contexts and cultures, with the role of parents an example. Mahfuza Rahman, 19, a member of the project management committee at the Family Planning Association of Bangladesh, told of the success of its Tarar Mela scheme, where young people could attend centres that offer training in computing and English, as well as contraception and sexual health advice, without their parents suspecting they were seeking information on sex.

But Chiboola Kabbudula, also 19, a peer educator and national executive member of Planned Parenthood Association of Zambia, suggested mothers could play an important part in giving advice. "You need to talk to your mother, explain to her: 'Mummy, I'm beginning to feel this way, I think I need this service'," she said. "[Your mother] will not stop you from going because she understands you as a grown-up woman."

O'Brien said Kabbudula's account was a useful lesson for the summit's delegates. "We ought to remind ourselves that our preconceived notions are almost invariably wrong," he said. He rejected the idea of donors making aid conditional, but there was agreement that the progress of nations receiving funding should be monitored closely. "All of us are trying really hard to get to a results agenda," he told the campaigners at the table, "so that you have this chance to chase the people you're trying to hold to account."

Making contraception available was not encouraging young people to have sex, concluded the IPPF's director general, Tewodros Melesse. "Do you buy insurance for your car so you can go and smash yourself? No, it's just in case." Contraception was the same. "When you are not prepared to have a child and you have chosen to have sex, or you are forced to have sex," he said, "you need the contraceptive so things don't happen by accident."

At the table

• Sarah Boseley (chair), health editor, The Guardian

• Stephen O'Brien, parliamentary under-secretary of state for international development

• Tewodros Melesse, director-general, International Planned Parenthood Federation

• Mahfuza Rahman, member of project management committee, Family Planning Association of Bangladesh

• Doortje Braeken, senior adviser of adolescents and youth, International Planned Parenthood Federation

• Chiboola Catherine Kabbudula, Planned Parenthood Association of Zambia

• Audrey Simpson, director of Northern Ireland, Family Planning Association

• Tonte Ibraye, national co-ordinator, White Ribbon Alliance, Nigeria

• Joe Cerrell, European director, Bill & Melinda Gates Foundation

• Roger Ingham, professor of health and community psychology, University of Southampton

• Simon Blake, chief executive, Brook

• Anna Martinez, co-ordinator, Sex Education Forum

• Yasmin Ahmed, senior regional director, Asia, Middle East and eastern Europe, Marie Stopes International

Roundtable report commissioned and controlled by the Guardian. Discussion hosted to a brief agreed with the International Planned Parenthood Federation. Paid for by the International Planned Parenthood Federation. Contact Mark Lacey 020 3353 3727 for information on roundtables or visit theguardian.com/sponsored-content