Editing permissions


I am requesting some addon that only allows a specified usergroup to edit posts posted by that usergroup, so for example:

Registered users - Can not edit posts
Level 1 - Can edit posts by level 1 and below.
Level 2 - Can edit posts by level 2 and below.

This is because we allow Level 2 (highly trusted members) to post HTML, but we don't want any Level 1s to be able to edit the HTML posted by Level 2. If there is any add-ons like this around, I'd appreciate if you could link me.