Wikipedia has a list of people killed by police in the UK. If you discount the ones that happened in Northern Ireland during The Troubles, it has a grand total of 15 people killed by police since 1920.
I do not feel scared by that number.
I'm not sure which numbers you were looking at, but I think they are rather a lot higher than that, even if not officially acknowledged as such. Possibly you have confused "being shot by the police" with "being killed by the police" (although even then the number is far, far higher than that).
Between 2000 and 2011 there were nearly 6,000 deaths in police custody in the UK. Now, some (perhaps even many or most) of those will be unavoidable - perhaps people who would have died anyway even if not in police custody. Then, some are down to negligence (although I'd argue that in many case that is just as bad as malfeasance - if I was at home and vulnerable to some medical condition e.g. diabetes then it's much more likely someone would be around who would watch and look after me properly). But I find it very difficult to believe that given such a large number of cases there is no significant element of either bad intent or intentinoal recklessness, because it really is a shockingly high number - for context, it is not terribly far off the total number of murders recorded in the UK in the same period.
Looking just at shootings - there seem to be on average about 6 or 7 a year in recent years - e.g. here is a list of some of them. There are in fact multiple recent cases where the police have literally shot naked and unarmed people (and faced only relatively minor consequences as a result) and several more where they have shot unarmed people. Even in this case, which would appear to be about as clear-cut a case as they come, the officers were acquitted and retained their jobs in the police, albeit not on firearm duties.
Finally, I'd like to say that the fact that police can apparently get away with murder should worry you, for two reasons. Firstly - not because you might be murdered by the police yourself (that is still very unlikely), but because it means they might be likely to get away with far lesser crimes (like assaulting you, planting drugs on you, or making up a traffic offence because they decide they don't like the look of you) much more easily. Secondly - because it is indicative of a force who don't see their primary loyalty as being to the victims of crime (and to thus solving crime) but rather to looking after their own. If you were a victim of crime, would you want a force where the officers thought people who didn't pull their weight to solve it effectively should be protected from public scrutiny?
If anything, we should be holding police officers, especially firearms officers, to a higher standard than we do the general public because we grant them additional powers and privileges and entrust them to use those responsibly while paying them out of the public purse.