brassmonkey,
I am familiar with the situation you describe, although it is largely historical and related to those units who started with Squirrels and then moved onward and upward. It was only applicable to those units that held PAOCs that included the Squirrel. In fact, most of those units gave up doing that some while ago. It was costly in continuation training and currency atrophied. Also, the supply of police equipped Squirrels dried up. I may be wrong, but I believe that PSNI never operated Squirrels under their PAOC, and so probably do not have the AS355 on their PAOC. An ASU cannot operate a type unless they have it on their PAOC.
For a few years now it has been very difficult to get hold of police Squirrels because there was little demand. I think G-SEWP is/was one of the few available. Where Squirrels have been used, they need to be bought in with an associated PAOC and pilots. In these circumstances, the pilots may not be as experienced as you suggest. I was only mentioning this, as the post previous to mine implicitly assumed that the accident aircraft was flown by PSNI pilots, which might not be the case.
Undoubtedely, it is good news that no one seems to have been seriously injured.
I believe the AS355 was leased in addition to the PSNI machines in any case. So they would need extra pilots.