A London solicitor, born near Malton, Yorks, he was appointed WM connexional legal adviser in 1803 and was the brain behind the Committee of Privileges, set up that year to protect nonconformist rights under the Toleration Act. His advice to Jabez Bunting in 1810 on the reorganization of various aspects of Methodist administration had a lasting influence on the development of the connexion. He came into national prominence in countering the Sidmouth Bill of 1811, which would have effectively ended local preaching. Helped by Joseph Butterworth and Thomas Thompson, Allan produced 700 WM petitions containing 30,000 signatures and the Bill was 'killed'. He also master-minded the new Toleration Act of 1812 (52 George III c 155), which was important for all the Free Churches. He drafted a new Model Deed and advised Bunting on Mission administration, the education of the preachers and general Conference legislation.
Ardently Protestant, he was a leading member of the Protestant Union, founded in 1813, and opposed Catholic Emancipation in 1829 and grants to Catholic schools. He was Master of the Haberdashers' Company in 1838. As a local preacher he was content to preach to the poor in the workhouses and smaller chapels. He had been an ally of Bunting, but their paths diverged and his role in the consolidation of WM came to be much under-estimated figure until reassessed by recent scholaship in the light of his papers in the connexional Methodist Archives. He died at Brighton on 26 September 1845.
His wife Esther was the daughter of Thomas Robinson, merchant and ship-owner, who was a prominent member of the Methodist society at Bridlington. Their son, T.R. Allan, was also a solicitor.
'To promote this [the 1812 Toleration Act] he waited on all the leading members of both Houses of Parliament. Earl Grey listened to his argument and then said: "Don't you think, Mr. Allan, that Methodist preaching ought to be placed under Parliamentary restraint?" The lawyer simply answered, "No, my Lord, I think it ought not; but rather to be protected and encouraged as a national benefit."' (London Quarterly Review, October 1885, p.123)