@123kingarthur See @k89bpa s answer. Many many countries make up the commonwealth. The two who murdered Lee Rigby were from a commonwealth country originally and became naturalised citizens of Britain before going on to murder Lee Rigby.
We really do need to let go of these rose tinted views from the past. Immigration should be based on merits and need. Just as we have people that do bad things we do just have to accept that every other country has bad people too and sometimes they slip through the system.
A brilliant link was posted the other day to this article: