Religious and anti-abortion groups have been holding a rally to mark 40 years since abortion was legalised.
Activists want abortion laws to be changed
Activists met at the Houses of Parliament to call for a reduction in the upper time limit for abortion.
They later walked to Westminster Cathedral for a service commemorating 6.7m abortions performed since 1967.
Marie Stopes International said that although abortion rates needed to come down, the 1967 act had made it safer for women to terminate pregnancies.
Campaigners against abortion began their protest on Friday night when they projected the number of abortions on to the riverside face of the Houses of Parliament.
In the 40 years since abortion has been legal in Britain, the number of terminations taking place each year has increased from 22,000 to almost 200,000.
However, on Wednesday Health Minister Dawn Primarolo said the government did not believe there is sufficient scientific evidence to lower the legal abortion limit of 24 weeks.
Julia Millington, political co-ordinator for Alive and Kicking, the pro-life alliance organising Saturday's events, said the campaign was intended to raise awareness of the rising number of abortions and call for a change in the law.
She said nothing had persuaded the Department of Health that survival rates had improved for extremely premature babies born before that time.
She said: "We believe there is increasing public concern about these latest figures and we want to draw attention to this anniversary."
Lord Steel, who piloted the 1967 act, suggested he would like to see lower abortion rates, but he said there was no such thing as a "correct" number and that each case had to be considered "on its merits".
Freedom to choose
Dr Kate Worsley, of sexual healthcare provider Marie Stopes International, agreed that more had to be done to bring rates down, such as providing better sex education and provision of contraceptives.
"But the main point is that they're safe, whereas [in] about 50% of countries in the world, women are still having unsafe abortions," she added.
Dr John Parsons, of the British Pregnancy Advisory Service, told BBC News 24 that, above all, the act had given women choice.
"It has meant that for the last 40 years women have had the option to end pregnancies which are unplanned and which they do not wish to continue.
"It has given them freedom and independence."