Members of the British Army swear allegiance to the monarch as their commander-in-chief, but the Bill of Rights of 1689 requires parliamentary consent for the Crown to maintain a peacetime standing army. The term British Army was adopted in 1707 after the Acts of Union between England and Scotland. The modern British Army traces back to 1707, with an antecedent in the English Army that was created during the Restoration in 1660. As of 2021, the British Army comprises 82,230 regular full-time personnel and 30,030 reserve personnel.

The British Army is the principal land warfare force of the United Kingdom, a part of the British Armed Forces along with the Royal Navy and the Royal Air Force.