The parish church of the Holy Trinity is of exceptional interest because of its rare date. It was built between 1650 and 1652 during Cromwell's Protectorate or Commonwealth, on the instruction of George Fenwick, Governor of Berwick, to the designs of John Young of Blackfriars, a London mason. It replaced the medieval church which had stood a few yards to the south since 1190AD and which was demolished shortly after the new church opened. The Holy Trinity was one of only a few churches built in England in Cromwellian times.
The Cromwellian regime was strongly influenced by puritanism and as a result the building was of a simple design to the point of being plain, with a mixture of Gothic and Classical styles. It was constructed from stone and timber from the 13th century Castle of Berwick upon Tweed and had no bell tower, originally no ornamentation or even stained glass; a bell in the Town Hall is used to summon people to the church services. The stained glass present in the church today includes 16th century Flemish Roundels previously sequestrated by Charles I from The Duke of Buckingham. The unique Reredos is an early work by Sir Edwin Lutyens. In 1855 the chancel and clerestory windows were added- the western turrets may have also been added at this date. The church has strong historical connections to the Coldstream Guards, who were originally formed in 1650 as Monk's Regiment of Foot: one of the early officers associated with them was Fenwick.