The Centre for Applied Science and Technology (CAST), formerly known as the Home Office Scientific Development Branch (HOSDB), is responsible for UK body armour standards.
Their 2017 publication is 92 pages long and outlines the minimum performance requirements and test methods for body armour intended for UK law enforcement agencies.
There is currently no standards or legal required testing for civilian body armour which is why the market is flooded with cheap options that lack accreditation.
Specifically the publication details the following protection levels (may not display correctly on mobile).
Ballistic Protection Levels (page 35)
|Level||Calibre||Test Round||Bullet mass||Min Range||Max BFS (mm)||Single BFS limit (mm)||Velocity (m.s-1)|
|HO1||9mm FMJ||MEN 9 mm FMJ DM11A1B2||8.0g (124gr)||5m||n/a||44||365 +/- 10|
|9mm JHP||Federal Premium 9 mm JHP P9HST1||8.0g (124gr)||5m||n/a||44||365 +/- 10|
|HO2||9mm FMJ||MEN 9 mm FMJ DM11A1B2||8.0g (124gr)||5m||n/a||44||430 +/- 10|
|9mm JHP||Federal Premium 9 mm JHP P9HST1||8.0g (124gr)||5m||n/a||44||430 +/- 10|
|HO3||Rifle 7.62 calibre||Radway Green 7.62 mm NATO Ball L44A1 or L2A2||9.3g (144gr)||10m||25||30||830 +/- 15|
|Rifle 7.62 calibre||7.62 × 39 mm surrogate||7.9g (122gr)||10m||25||30||705 +/- 15|
|HO4||Rifle 7.62 calibre||SAKO .308 Win 480A Powerhead or Barnes .308 TSX BT||10.7g (165gr)||10m||25||30||820 +/- 15|
|SG1||Shotgun 12 gauge True Cylinder||Winchester 1 oz. Rifled 12RSE||28.4g||10m||25||30||435 +/- 25|
What does this mean?
As an example, protection level HO1 should stop a 9mm bullet from a minimum distance of 5 metres at a speed of 365 metres per second. There should be a maximum Back Face Signature (BFS) of 44mm.
The BGS is the maximum depth of indentation made by body armour into ballistic backing material after impact, measured perpendicular from the surface of the backing material. This is important as body armour could stop a strike but the indentation left by it could be so great that the impact could seriously hurt your internal organs.
Stab and Spike Protection Levels (page 58)
|Level 1||Level 2|
|Level||Energy (J)||Max Penetration (mm)||SPL (mm)||Energy (J)||Max Penetration (mm)||SPL (mm)|
|KR1 + SP1||24||KR1 - 8, SP1 - 0||KR1 - 9, SP1 - 0||36||KR1 - 20, SP1 - n/a||KR1 - 20, SP1 - n/a|
|KR2 + SP2||33||KR2 - 8, SP2 - 0||KR1 - 9, SP2 - 0||50||KR2 - 20, SP2 - n/a||KR2 - 30, SP2 - n/a|
What does this mean?
Stab is KR and Spike is SP.
At Knife Resistance Level 1 (KR1) and Spike Resistance Level 1 (SP1), at a force of 24 joules the knife only can penetrate the armour to a maximum depth of 8mm. A single maximum penetrable depth of 9mm depth is allowed. The spike is not allowed to penetrate.
At a force of 36 joules the knife only can penetrate the armour to a maximum depth of 20mm. A single maximum penetrable depth of 20mm depth is allowed. The spike is not allowed to penetrate.
There’s far more contained within the Home Office Body Armour Standards than just the protection levels. The requirement for a Declaration of Construction, labelling on armour and more explains in detail what you should look for when purchasing body armour.
External Reference: Home Office Body Armour Standards