There are several different assault rifles - both by the true definition of an assault rifle and by the political motivated BATFE definition of a so-called "civilian assault rifle", manufactured by several different outfits. Which assault rifle did you have in mind, specifically?
The SKS is not an assault rifle, nor even a BATFE-defined "civilian assault weapon". And no, a permit is not required.
Check amazon.com.
One cannot legally purchase an assault rifle anywhere in the UK. In the UK one may buy certain firearms, notably shotguns, but there are strict conditions attached to ownership.
No. The function of it is what makes it an assault rifle. An assault rifle fires an intermediate cartridge and has a select fire option (either auto or burst). In the political sense, the determination of what made a so-called "civilian assault weapon" was determined by the BATF (now BATFE) based on the presence of two or more cosmetic features (such as bayonet lugs, pistol grips, and flash suppressors).
You can buy a semi automatic Title I rifle at 18. To purchase a true, select fire (auto or burst) NFA tax stamped assault rifle, you must be 21.
An actual assault rifle has select fire (semi and auto and/or burst fire). This was not used. The term coined by the Clinton administration is "civilian assault weapon", and was defined by the presence of two or more cosmetic features (e.g., bayonet lug, flash suppressor, collapsible buttstock, pronounced pistol grip). Connecticut in 2004 wrote the Clinton ban into state law after the ban went into sunset. An AR type rifle was used, but it was a ban compliant, single feature rifle, thus it would not into the BATFE definition of a "civilian assault weapon".
The M16 assault rifle is chambered for the 5.56x45mm NATOcartridge. It can also fire the civilian .223 Remington round.
Assault rifle.
The M16 assault rifle is chambered for the 5.56x45mm NATOcartridge. Most can also fire the civilian .223 Remington cartridge.
The SOAR (Special Operations Assault Rifle).
The first true assault rifle debuted in 1942.