Hi Ella

This is how I see it  (but would like to see any opposing views)

2C would be comparable
5+ clubs is "more precise" than 2+

And the point range for an overcall would be "similar" to that of an opening bid
Unless the pair has an agreement where an overcall can be significantly less than an opener (meaning less than 10 points)

If a jump overcall is strong (or intermediate) 3C would also be comparable

A bid of another suit or  pass or double would not be comparable because there are possible features of the replacement call which are excluded in the out-of-turn 1C opening

A tricky one is if West bids 1NT now
I think that would NOT be comparable (assuming 1NT opening and overcall are similar point range) because the failure to open 1NT then shows somethng different than the 1NT overcall

So if the 1C bidder didn't have a club suit good enough to overcall there would be no comparable call available

thanks nick.   would W need to have 4+ clubs to call 2C ie if only 2???

As I see it the offender (West) is free to make any call in this situation
So to bid 2C counts as comparable and the bidding continues normally even if 2C is "wrong" according to their methods

A "wrong" bid is not illegal unless it comes into the "illegal psyche" category
So if West overcalls 2C  with only 3 clubs (or 2 clubs - which would be a psyche) and gets lucky the opponents have no redress

gee, thanks giles.  I shall make that my bedtime reading, but it is similiar to the group of directors that I polled when this first arose - none could agree