Prior to the Great Fire of London of 1666 the old tower had a ring of five bells, a small sanctus bell and a clock bell. Following the completion of the new tower, a ring of eight bells was cast by Richard Phelps of the Whitechapel Bell Foundry. Between 1714 and 1718 the ring was increased to ten with the addition of two trebles. The first peal was rung on 15 February 1724 of Grandsire Caters by the Society of College Youths. The second bell had to be recast in 1748 by Robert Catlin and the tenor was recast in 1831 by Thomas Mears of Whitechapel, just in time to ring for the opening of the new London Bridge. In 1843, the treble was said to be “worn out” and so was scrapped, together with the sanctus bell, while a new treble was cast by Thomas Mears. A new clock bell was erected in the spire in 1846. This bell can still be seen in the tower from the street.
The 10 bells were removed for safe keeping in 1940 and stored in the churchyard. They were taken to Whitechapel Bell Foundry in 1951 whereupon it was discovered that four of them were cracked. After a long period of indecision, fuelled by lack of funds and interest, the bells were finally sold for scrap in 1976. The metal was used to cast many of the Bells of Congress that were then hung in the Old Post Office Tower in Washinton, D.C.
A fund was set up on 19 September 2005 under the leadership of Dickon Love with a view to installing a new ring of 12 bells in the tower in a new frame. The money was raised and the bells were cast during 2008/09 by the Whitechapel Bell Foundry. The tenor weighed 26cwt 3qtr 9 lbs (1360 kg) and the new bells were designed to be in the same key as the former ring of ten. They were consecrated by the Bishop of London on 3 March 2009 in the presence of the Lord Mayor of London and the ringing dedicated on 26 October 2009 by the Archdeacon of London. The bells are named (in order smallest to largest) Michael, Margaret, Thomas of Canterbury, Mary, Cedd, Edward the Confessor, Dunstan, John the Baptist, Erkenwald, Paul, Mellitus and Magnus. The bells project is recorded by an inscription in the vestibule of the church.
The first peal on the twelve was rung on 29 November 2009 of Cambridge Surprise Maximus. Other notable peals on the new bells include a peal of Stedman Cinques on 16 April 2011, St Magnus Day, to mark the 400th anniversary of the granting of a Royal Charter to the Plumbers’ Company, a peal of Cambridge Surprise Royal on 28 June 2011 when the Fishmongers’ Company gave a dinner for the late Prince Philip, Duke of Edinburgh at their Hall on the occasion of his 90th birthday, and a peal of Avon Delight Maximus on 24 July 2011 in solidarity with the people of Norway following the tragic massacre on Utoeya Island and Oslo. In 2012 peals were rung during the Thames Diamond Jubilee Pageant on 3 June and during each of the three Olympic/Paralympic marathons, on 5 and 12 August and 9 September. Following the announcement on 9 April 2021 of the death of Prince Philip, Duke of Edinburgh the tenor bell was tolled 99 times.