William Allen FRS FLS FGS (29 August 1770 – 30 September 1843) was an English scientist and philanthropist who opposed slavery and engaged in schemes of social and penal improvement in early 19th-century England.

Allen had concentrated on his own career in the field of pharmacy, taking over the Plough Court chemical business of Joseph Gurney Bevan who retired in 1795.

A year later he was made president of the Physical Society at Guy's, and on the advice of Humphry Davy and John Dalton also accepted an invitation from the Royal Institution to become one of its lecturers.

This strengthened his ties with the eminent Humphry Davy, and in due course with his long-standing friend Luke Howard, who was likewise elected to Fellowship of the Royal Society, though some years later.

As a teenager, under the influence of Quaker abolitionists, Allen gave up sugar as a reaction to the Atlantic slave trade and abstained from it until 1834.

All the members of its predecessor committee (1783–1787) had been Quakers, and nine of the twelve founders of the subsequent non-denominational Society for the Abolition of the Slave Trade were Quakers, including two – Samuel Hoare Jr and Joseph Woods Sr (father of the botanist Joseph Woods Jr) – who lived close to William Allen in Stoke Newington, the village near London where Allen had family interests after his second marriage in 1806.

Wilberforce visited William Allen at his experimental gardens on several occasions in his role as the Society's parliamentary representative.

His sister Sarah had married the lawyer James Stephens, whose family home was the Summerhouse, a large house adjoining Abney Park in the very grounds of the mansion that later, in the 1820s, was to become Allen's novel girls' school.

William Allen was also a founder member and a Director of the African Institution, the successor body to the Sierra Leone Company, sponsored by philanthropists to establish a colony in West Africa for slaves freed on a voluntary basis, through the abolitionists' efforts, in America.

Mr Allen was indefatigable in his efforts, by interviews with Ministers and official persons.. His account of the spirit-stirring time is graphic:" In 1838, the Friends sent a party to France.

Allen made an approving note in his diary, during 1798, on a pacifist tract, The Lawfulness of Defensive War upon Christian Principles Impartially Considered.

[2] In the area of penal reform, prompted by Basil Montagu, he founded a Society for the Diffusion of Knowledge Respecting the Punishment of Death and the Improvement of Prison Discipline, in 1808.

Using only small plots, he carried out trials at Lordship Lane in Stoke Newington, and later put into practice some of his findings at the model agricultural settlement of Lindfield that he helped establish.

[21] Allen was approached to help fund the ideas of Joseph Lancaster and his monitorial system, under which one teacher supervised several senior pupils, who in turn instructed many junior ones.

It was also innovative in commissioning the world's first school bus, designed by George Shillibeer, to transport the pupils to Gracechurch Street meeting house on Sundays.

Grizell was the eldest sister of another family of well-off Stoke Newington Quakers, of whom the best-known is Samuel Hoare Jr (1751–1825), one of the twelve founding members of the Society for the Abolition of the Slave Trade.

As a wealthy widow, she contributed to the 1824 foundation of Newington Academy for Girls, and three years later she and William Allen, both co-founders of this novel educational establishment, married.

William Allen died on 30 December[27] 1843 and was buried in Stoke Newington, London, in the grounds of the Yoakley Road Quaker Meeting House.

Today this has been replaced by a Seventh-Day Adventist chapel, the other half of its grounds becoming a small Council-maintained park for the nearby public housing estate.