It seems therefore that, after the initial call, if ATC does not have the time to respond more fully, there are two options:
1. If there is a stated or implied request to enter CAS, the reply should conform fully to the above and include a time of expected clearance and a time check ... or,
2. If there is no stated or implied request to enter CAS, a simple "Stand-By" should suffice.
... nuff said?
Err, that's what I said .... (highlighted below)
There is no assumption needed if the pilot states on his first call what his reqeuest actually is, as per the CAP413, i.e. flight information service (no request to transit CAS is needed), joining instructions (requesting permission to enter controlled airspace to land at an airfield within it), or a controlled airspace transit. In the latter two cases, the arse covering is required if an immediate clearance to enter can't be given, in the former I would think that ATC could intelligently omit the phrase. In my experience when operating as GA pilot, this is more often than not the case.