When the "Black and Tans were deployed to Ireland in the early 1920's they were still in the UK as all of Ireland was still part of the UK.
The politicians at Westminister approved of their formation and terms of service.
As there was a war on and the civil power could not cope, ex soldiers were recruited to support the RIC.
It was sad that discipline did break break down and members (how many?) over reacted.
There is a very good possibly that your relative behaved in a civilised manner.
I have tried to be realistic but I have probably annoyed some one.
In summary if the politicians cannot sort things out they get some one else to "police" the issue and they sit back and the poor old "Tommy" gets the blame when things escalate.