The British starstreak missile is the most lethal British weapon currently in use in Ukraine.

According to security analyst, the British Starstreak Missile is the world’s quickest short-range air defense missile, and it’s already been credited with downing a Russian Mi-28 helicopter in Ukraine during its maiden deployment.
Watch video of the downing of the Russian helicopter below;
In the above video, the British Starstreak Missile, a high-velocity weapon with three kinetic darts that destroys targets, can be seen slicing the helicopter in half above the Luhansk region in eastern Ukraine.
After Ukrainians using British techniques opened fire, the tungsten spears broke the tail off the Mi-28N, according to the footage from the battle.

According to sources, the anti-aircraft system has been stationed in the country for more than a week. Senior defence industry sources who examined the above footage also believe it to be the weapon.
The Starstreak system is a laser-guided missile that can knock down low-flying enemy jets and attack helicopters at more than three times the speed of sound.
According to sources, the United Kingdom is supplying and training Ukrainian troops in the use of the high-velocity anti-air missiles, as well as body armor, helmets, and combat boots.
Prime Minister Boris Johnson has stated repeatedly that the United Kingdom will continue to give defensive assistance to Ukraine, including a new supply of 6,000 missiles.