Violent crime is an issue far too complex to be boiled down simply to firearm restrictions when examining different countries. In looking at various countries, one will find that many with stricter firearms laws than the U.S. do indeed have lower violent crime rates, some are nearly identical, and some are actually higher. Likewise, if you look at nations which have similar or less restrictive firearm regulations than the U.S., you'll find the same lack of correlation.
What is more useful, and the U.S. is somewhat unique in this respect, is comparing the violent crime rates of different regions of the same country with varying gun laws. Here in the U.S., states with comparatively relaxed gun restrictions generally have similar or lower violent crime rates than states with stricter gun laws. Even more telling, states which ease certain restrictions, particularly those on the carrying of handguns outside the home, typically experience reductions in violent crime after the restrictions are eased.
What it boils down to is this, every law passed removes some degree of freedom from the people; sometimes the degree of freedom lost is small and sometimes it is great depending on the restrictiveness of the law. Where the disagreement lies is where the amount of freedom lost outweighs the benefit of the law. Most people in the U.S. agree that the benefit of requiring a criminal background check prior to buying a gun is worth the small reduction in freedom associated with it. However, most of the U.S. populace would also say that the benefit of banning handguns is not worth the reduction in freedom that is associated with it.
As far as the gun laws of the U.K., my opinion is this: the degree of restriction placed on firearm ownership in Britain does most likely make guns less available to the criminal element when compared to the U.S. However, that same degree of restriction also severely limits the ability, and therefore freedom, of the people to defend themselves. Self-defense is a concept that I view as a basic human right and, as such, I feel that the loss of freedom associated with U.K. gun laws outweighs the benefits associated with them.
As to less lethal alternatives such as pepper spray, stun guns, and tasers (I personally hate the term "non-lethal" because any weapon capable of disabling an attacker with any degree of reliability can be lethal under the right circumstances), they are good and useful, but they still have their limitations. Few would argue, I think, that a defender armed with pepper spray or a taser is at a distinct disadvantage when faced with an attacker armed with a firearm. This is why even though less-lethal alternatives have been embraced by law enforcement, they have not replaced firearms. Personally, I want a means of defense that is equal to or greater than an opponent's means of attack. The only way that I can even come close to ensuring that is to have a firearm.
Smith, and Wesson, and Me. -H. Callahan
Well waddaya know, one buwwet weft! -E. Fudd
All bad precedents begin as justifiable measures. -J. Caesar