By John Bingham and Rebecca Smith
Official figures show that more than 21,000 girls under 18 chose to have a termination in 2007, the first time the proportion has reached 50 per cent.
Abortion providers described the landmark as a "positive sign" but pro-life campaigners said it was "frightening".
The number of under 16s getting pregnant leapt by 6.4 per cent, the figures from the Office for National Statistics show.
Meanwhile the overall rate for all girls under 18 rose for the first time since 2002.
It means that a Government target to halve the number of teenage pregnancies by next year now looks almost certain be missed despite intense efforts to promote contraception and more sex education in schools.
The figures come amid the furore over 13-year-old Alfie Patten, the schoolboy from Sussex who is said to be the father of his 15-year-old girlfriend Chantelle Stedman's daughter, Maisie Roxanne.
Among girls under 18, the conception rate increased from 40.9 per 1,000 in 2006 to 41.9 in 2007 - the first such increase since 2002.
When those under 16 were considered the rate rose from 7.8 per to 8.3 per 1,000 - an increase of more than six per cent in numerical terms - from 7,826 to 8,196 in 2007.
The proportion having an abortion rose to 50 per cent from 48 per cent in 2006 and as low as 40 per cent in 1996.
Ann Furedi, chief executive of the charity the British Pregnancy Advisory Service (BPAS), the UK's largest abortion provider, said: "The fact that half of the teenagers in this position felt able to end their pregnancy in abortion is actually a positive sign."
She described the fact that there is less social stigma among young people about having an abortion as "an entirely good thing".
But Josephine Quintavalle, of the ProLife Alliance, said: "I think that is just utterly offensive ... I don't know how any woman could say that."
Norman Wells, director of the Family Education Trust, added that the figures showing rising numbers of teenage pregnancies were just the "tip of the iceberg" and showed that the Government's teenage pregnancy strategy had been a "disaster".
Annette Brooke, the Liberal Democrat Children Spokesperson described the teenage pregnancy rate in Britain as "scandalously high" and said that earlier progress appeared to be being reversed.
"Instead of endless reviews and leaflets for parents, ministers need to ensure that all of our young people are getting the relationship and sex education they need," she said.
Andrew Lansley, the Conservative Shadow Health Secretary, said: "This is another Government target missed.
"Once again it demonstrates how pointless it is to set targets if the Government doesn't do what is needed to deliver on them."
The Government responded by announcing an extra £20.5 million to promote contraception in skills including a £7 million media campaign.
Beverley Hughes, the Children and Young People's Minister, admitted that the figures were "disappointing" and said that policies were being implemented in a patchy manner.
"There is no doubt that rates have come down where local areas have implemented the strategy properly, even in deprived areas," she said.
"The evidence suggests that more teenagers may have been engaging in risky behaviour and not using contraception, resulting in an increase in conceptions leading to abortion.
"Our strategy is to encourage teenagers to delay early sexual activity, but to use contraception when they do become sexually active."Original here