The regiment was formed as a 'large regiment' on 31 December 1966 by the amalgamation of the four remaining regiments of the Home Counties Brigade as a consequence of the Defence Review of 1957.The four regiments formed four battalions, retaining their previous names in the titles.

These were:

1st Battalion (Queen's Surreys) -- formerly The Queen's Royal Surrey Regiment (2nd, 31st & 70th Regiments of Foot).

2nd Battalion (Queen's Own Buffs) -- formerly The Queen's Own Buffs, The Royal Kent Regiment (3rd, 50th & 97th Regiments of Foot).

3rd Battalion (Royal Sussex) -- formerly the Royal Sussex Regiment (35th & 107th Regiments of Foot).

4th Battalion (Middlesex) -- formerly the Middlesex Regiment (Duke of Cambridge's Own) (57th & 77th Regiments of Foot).