The mid-nineteenth century was a rather odd time. Despite the French being allied with the British during the Crimean War, old suspicions died hard and the threat of invasion seemed real enough to cause much concern - especially with defence-related matters.
Much like today's TA (from which it is descended) the Volunteer Force were a part-time quasi-private army of willing and enthusiastic patriots that were formed to counter such an eventuality.
In 1859 authorisation was given for the raising of artillery, engineer and rifle corps at county level. These units were of local content and did not come under the authority of the War Office but rather the respective county's Lord Lieutenant. They were totally distinct from the Regular Army and the auxiliaries of the Yeomanry and Militia and their uniforms and equipment (much of it privately purchased) reflected this.
Rifle clubs were very popular at the time and for many clubs the transition to military unit was relatively simple - most members being from the middle and upper classes and thus sufficiently solvent enough to equip themselves as necessary - some units as mounted infantry. Weapons were privately purchased albeit under government approval to ensure commonality. It was an expensive hobby, though much money was raised by public donation.
The uniforms were designed by the units themselves - rifle green and grey being popular in lieu of scarlet in the infantry units and blue for the artillery. By today's standards it was a Walt's dream!
The purpose of the Volunteer Rifle Corps was pretty much like that of the Home guard during WW2 - each 'corps' being at company strength with detached platoons. The artillery and engineer elements were at battery and troop strength and were used to man the many defensive forts that protected key coastal points and port entrances. The gunners manned the guns and the engineers (submarine miners) crewed the apparatus used to deploy the sea mines.
By the early 1860s the VF numbered well over 150,000 and many units were reformed at battalion strength for ease of administration - weapons & equipment now being subsidised by the government, provided specific criteria were met - much like the modern bounty but at unit level.
The expanded units also saw the need for more uniformity in appearance, as each company was dressed differently than the other and a more standard appearance was introduced, though still at county level - much like regular battalions though still in distinctive VF livery.
Also at this time an act was passed that clarified the terms & conditions of service and emergency embodiment. The Volunteer Act of 1863 giving first real indication of the intent to integrate the VF within the armed forces proper.
In 1872, the status the Volunteer Force changed when command was transferred from the county lieutenancies to the War Office. This enabled fuller integration within the order of battle and the units enjoyed affiliation with their regular counterparts.
The Childers Reforms of 1881 saw the termination of the numbering system for infantry regiments and the birth of named county units with integrated auxiliary battalions of both Militia and Volunteers. The volunteer battalions of the VF and their artillery & engineer equivalents were now fully formed with 'parent units' of the Regular Army - a system that exists to this day.