The prime minister says he wants to promote competitive sport instead of targets that can become a 'box-ticking exercise'

David Cameron has defended the decision to scrap compulsory targets for the minimum number of hours of physical education in schools, saying it had been a box-ticking exercise that discouraged schools from doing more sport.

The prime minister said the key to the regeneration of sport in schools was the return of competitive sport: "We need a big cultural change in favour of competitive sports. I think that is what really matters."

Questioned over whether the education department had removed the requirement, introduced by Labour, for two hours of compulsory physical education every week in schools, he told LBC radio: "Every school has to deliver sport. What the last government did – which is not right – is if you just sit there in Whitehall and set a target but don't actually do anything to help schools to meet it, you are not really solving the problem.

"In fact, by just saying, 'I want you to do this number of hours a week', some schools think 'right, as soon as I have met that minimum target, I can tick a box and give up'." He also urged more teachers to give up their free time to teach sport as well as their main teaching subject. "The problem has been too many schools not willing to have competitive sport and some teachers not willing to join in and play their part."

He was speaking on LBC radio in the wake of the huge Olympics success, and a growing political debate on the role of schools in generating sporting prowess. The mayor of London, Boris Johnson, claimed that the success of the Olympics had been a Conservative lesson in showing the link between effort and achievement, as well as the role of competition.

Cameron said in his conversations with successful athletes that he had been struck by how many had been drawn into sport by a teacher – such as a great geography teacher – who also inspired in them a passion for sport.

Cameron said sport was still part of the national curriculum and £1bn was being spent on sport in schools over four years: "If the problem is money it would be solved by money."

Cameron agreed, saying: "I would like to promote competitive sport – we need more competition, more competitiveness, getting rid of the idea of all-must-have prizes and you cannot have competitive sports days. We need a big cultural change in favour of competitive sports." . Cameron was questioned over whether the education department had removed the requirement, introduced by Labour, for two hours of compulsory physical education every week in schools. He said: "Every school has to deliver sport. What the last government did – which is not right – is if you just sit there in Whitehall and set a target but don't actually do anything to help schools to meet it, you are not really solving the problem.

"In fact, by just saying, 'I want you to do this number of hours a week', some schools think 'right, as soon as I have met that minimum target, I can tick a box and give up'."

The prime minister claimed that the best schools say they do not want targets but want to be challenged to do more.

He He also disputed recent figures obtained via a freedom of information request by the Guardian, showing 21 playing fields had been sold in the last two years. He said 14 of these schools had closed, four had become amalgamated, and four had sold some surplus pitches and used the proceeds to improve facilities. He added: "It was a mistake that playing fields were sold in the past, but they are not being sold any more."

Christine Blower, general secretary of the National Union of Teachers, said: "It's not because of teachers that funding for the school sport partnership has been so drastically reduced. Nor is it down to teachers that playing fields are being sold off, despite election promises.

"What we need is the support of government, not the shifting of blame. We know of many teachers who are spending time from their summer break taking children from their schools to the Games."

Malcolm Trobe, deputy general secretary of the Association of School and College Leaders, said: "The prime minister's criticisms of school sport are ill-informed, unfair and fail to recognise the huge contribution that many teachers make to sports in schools. Many teachers, not just PE staff, willingly give of their time to motivate and coach young people in a wide range of sports.

"The prime minister is right to emphasise the need to link clubs with schools but this is the government that two years ago removed the funding for probably the most successful school sports scheme ever. The 450 School Sport Partnerships were a national network of sports colleges that put specialist PE teachers to work with primary school pupils, linked schools with local sports clubs, brought high quality coaches into schools and promoted competitive matches. This scheme was devastated by the huge cut in its funding."

"If the prime minister is serious about wanting to enhance sport in schools the funding will need to be put in place to support those very willing teachers and coaches to deliver a lasting sporting legacy following the performances of our outstanding Olympic athletes".