The Regular Reserve largely consists of ex-Regular personnel who retain a statutory liability for service and are liable to be recalled for active military duty "in case of imminent national danger or great emergency".

[7] The RFR, in its original form as a separate grouping of trained ratings/ORs, ceased to be under the amended regulations of the Reserve Forces Act 1996.

Prior to this, a soldier was generally enlisted into the British Army for a 21 year engagement, following which (should he survive so long) he was discharged as a Pensioner.

The cost of paying pensioners, and the obligation the government was under to continue to employ invalids as well as soldiers deemed by their commanding officers as detriments to their units were motivations to change this system.

The size of the army also fluctuated greatly, increasing in war time, and drastically shrinking with peace.

Battalions posted on garrison duty overseas were allowed an increase on their normal peacetime establishment, which resulted in their having surplus men on their return to a Home station.

Among the other benefits, this thereby enabled the British Army to have a ready pool of recently-trained men to draw upon in an emergency.

The act of 1870 allowed a soldier to choose to spend time in the reserves after service with the colours.

[17][18][19] By 1900 the reservists numbered about 80,000 trained men, still relatively young and available to be recalled to their units at short notice in the event of general mobilisation.

By the end of March 1915 more than thirty infantry regiments would see their trained reserves drop below 100 men.

[2] British Army – "All male (but not female) soldiers who enlisted before 1 Apr 97 have a statutory liability for service in the Long Term Reserve until their 45th birthday.

Men and women who enlisted on or after 1 Apr 97 serve for a total of 18 years or until age 55, in the Regular Reserve and Long Term Reserve combined from the date of completion of their full time Colour service.

Long Term Reservists may only be recalled under Section 52 of the Reserve Forces Act (RFA) 1996, for home or overseas service, in case of imminent national danger or great emergency.