It was in fact out of Northolt.
I certainly don't think reminding pilots of an unusual (in terms of it not being the common "climb to altitude XXXX' ") vertical profile in the clearance is a bad thing. Especially if you have a high volume of crews going through that are perhaps not familiar with local SIDs. Yes, I know we all brief, but sometimes in this world of rushed turnarounds, things do get missed, and if including a simple phrase within a clearance sets alarm bells ringing and saves just one level bust a year, thats one potential catastrophy averted.
At BHX where the initial stopper is a Flight Level, it even gets put on the ATIS that initial climb is to a level, not an altitude (although admittedly only when we have v. low QNH or someone has had a level bust).
OAP: If in doubt, for God's sake ask!!! Even if it's on the R/T. We don't mind, honest.
Sound advice indeed Coracle, and sadly advice that is often overlooked for all sorts of reasons
OAP