Thanks for the replies, guys, I'm very glad I asked the question because I seem to have been labouring under a misapprehension all these years.
Just to confirm I've got it straight - if you tell us to maintain 280 kts, you don't mean "do it now", you actually mean "do it when you pass 10 000 or 12 miles"?
It's a bit different this side of the Pond, when a controller gives us a speed to fly here he means "do it ASAP" - he'd have a fit if we only did it in 5 minutes time! Yet another difference to put in my little black book!
Many thanks for all the replies.
t