Rifle used by the CCF, SCC, ACF and ATC; that is, the UK's military cadet forces.
It's based on the L85, better known as the SA80 (SA80 being the family of rifles) which most of the British Armed Forces use. The differences are that it is non-automatic, so has no change lever or gas parts and a much larger cocking handle, which also helps when it comes to very small cadets having to cock it.
Similarly to the L85, it takes a standard NATO magazine with 5.56 rounds (just like an M16). The magazine in theory holds 30 rounds, but most springs won't handle that so it's safest to fill 25-28.
The sights fitted to the L98 (as opposed to the L85) by default are the iron sights, because SUSATs are expensive and fragile and cadets don't need them.
Why train cadets with them? As mentioned above, most cadets start with some variety of .22 rifle, which are usually heavy and manual. In addition to being something that even the most desperate teenager would struggle to go on a rampage with, they are phenomenally easy to use (even the health-and-safety-obsessed manual doesn't require someone to have done a test before firing one) and are useful to teach marksmanship principles on.
The L98, on the other hand, is used for teaching cadets the fighting stuff, which is the reason most of them join to begin with. It fires blanks the same way it fires live rounds, so no extra training is needed for cadets to run around pretending to shoot stuff, other than a warning never to aim directly at something. Although no metal comes out the barrel when firing a blank, the hot air is dangerous and the official lethal range is usually quoted as 50m.
The L98 can also be used on an outdoor range, but isn't ideal for the purpose. The reason for this is that, because it is manual, the firer has to effectively reposition himself after every shot, which can be annoying. Despite this it is a very accurate weapon.