Misleading sentences:
In this country we don't deal in summary execution by a policeman without trial and conviction in the street, no matter what past offences we've committed.

Trials and convictions normally take place in the courts.

Let's also add in redundancy. If it is 'summary execution' then 'without trial and conviction' is redundant.

Also, we need consistency in the use of 'we' within the sentence. "We don't deal" appears to relate to the public, or this nation, but "past offences we've committed" appears to relate to the person 'executed' by the police.