Lock date of post publication

Hi all,

I’m looking to forbid anyone lower than an editor from changing the post publication date. So the date on a post should be locked and can only be changed by an Editor or an Administrator.

How can I go about achieving this? I’ve looked through the plugin database without too much luck.

Alternatively, how can I freeze the date of articles, making it completely unchangeable to anyone, including administrators, so the date will always equal when the article was first published?

Many thanks,
Michael