RE: What can you scrutinise
1) There is nothing stopping you from scrutinising the constitution, although your council may well have a Constitutional Working Group, or similar, a cross party formal/informal group with specific responsibilities for reviewing this document, so I'd check if such a body exists;
2) Issues relating to court cases cannot usually be considered by scrutiny when legal action is ongoing (the council may be considering an appeal, for example) but there should be no reason why members should not look at the issue once such action has been concluded to see if any lessons have been learned from the experience;
3) You have an absolute right to call in chief officers if you wish and I would be interested to see what reasons you have been given for prohibiting you from doing this;
4) You can get the police in, but only insofar as what you are asking them about relates to their role as a "responsible authority" on the Community Safety Partnership. That said, I can't see any fundamental problem with inviting senior police officers to speak to you on matters of general interest. I'd perhaps suggest contacting your police authority first to discuss the issue with them.
If you want to contact me directly I can be reached on 020 7187 7369.
Hope this helps,
Research and Information Manager, CfPS