[citation needed] Southwell was elected to the British House of Commons as a Whig Member of Parliament for Bridgwater on 28 March 1761, sitting until 1763.

[1] The Barony was previously held by Margaret Coke, Countess of Leicester (his maternal grandmother's youngest sister), who died on 28 February 1775.

Together they were the parents of one son and four daughters, including:[1] Baron de Clifford died on 1 November 1777 and was buried at Henbury, Gloucestershire.

[1] After his death, his widow, Lady de Clifford, was according to some accounts appointed Governess to Princess Charlotte, daughter of the future King George IV.

Peregrine Francis Cust, and of Mary Elizabeth Townshend, who married George James Cholmondeley, Receiver-General of Excise and secondly to Charles Marsham, 2nd Earl of Romney.