In late-1960 the RAF, impressed by the 'new' type of JP, made the crucial follow-on order, with 185 Jet Provost T.4's being requested from Hunting-Percival. The Mk.4 differed from the Mk.3 with a more powerful engine, the Armstrong Siddeley (later Rolls Royce) Viper 11 (Viper 201) being installed instead of the Viper 8 used in the earlier order. The rest of the airframe, apart from minor improvements was unchanged.

The first production aircraft of the order (XP547) was test flown on 4th August 1961 and, like the first examples of the T.3's delivered, sent to the Aircraft Armament & Experimental Establishment (AA&EE) at Boscombe Down for testing. This example was followed by further examples before being formerly introduced to the RAF training syllabus.

First deliveries of the Jet Provost T.4 began to arrive at RAF bases in November 1961 and the type gradually took over some of the roles that the T.3 was employed to do. The T.4, with the more powerful Viper, had extra thrust available, and that encouraged the RAF to utilise it in a number of different situations.

Training units that first adopted the type were the Royal Air Force College (RAFC) and the Central Flying School (CFS) and the type served alongside the existing fleet of T.3's. Deliveries also began filtering through to the various Flight Training Schools, with 2FTS based at RAF Syerston, 3FTS (RAF Leeming), 6FTS (RAF Acklington and Finningley) and RAF Church Fenton-based 7FTS all receiving examples between 1962 and 1964.
In addition, the College of Air Warfare, (CAW) based at RAF Manby also used the type during the 1960s until the station closed in the early 1970's.

During this period of time most RAF Squadrons had an aerobatics team, and the Jet Provost T.4 was the mount of some well-known teams. "The Red Pelicans" formed by members of the Central Flying School converted onto the T.4 after using the T.3 in previous years, and they were painted in an attractive all-over red colour scheme. There was also the College of Air Warfare's "Macaws" team based at Manby, that was seen at a number of airshows throughout the late 1960's and early 1970's.

Two other RAF Units were late users of the type, and were ultimately the last to employ the T.4 in service. Firstly the Tactical Weapons Unit (TWU) based at RAF Chivenor took on a small number of T.4s to help provide Air Controller Training for the UK armed forces. The other user was CATCS, the Central Air Traffic Control School based at RAF Shawbury.

Sadly the T.4 suffered major fatigue problems, which drastically reduced its time in RAF service and saw the type retired much earlier then planned. During the mid-1970's many of the T.4s reached their fatigue limits and were permanently grounded as a result. Some ended their lives as ground instructional airframes at RAF stations, and others being less fortunate were scrapped.
The airworthy survivors scattered around the Training schools with remaining fatigue lives were all sent to the CATCS at RAF Shawbury, and their places were taken by T.3s and T.3As. The T.4 served at RAF Shawbury for a while longer, but numbers were gradually reduced over the following 10 years, with the last few aircraft being finally retired in July 1989.

As the last T.4s were approaching completion at Luton the RAF realised that their high altitude training programmes were restricted because the Jet Provost T.4 was not pressurised. The British Aircraft Corporation (who had absorbed Hunting Percival during the mid 1960s) responded to this, and began to develop a new pressurised version as a private venture. To help them achieve this, they utilised the last two T.4s of the RAF order and began development work Time would tell if the RAF would be interested in adopting yet another variant of the Jet Provost.

The Jet Provost T.4 was exported to three countries, Iraq (20 aircraft), Venezuela (15 aircraft) and Sudan (8) aircraft. Yemen also took delivery of several refurbished RAF aircraft.