This thread dovetails with
this. I had another one the other day, inbound and routing up the west country - "descend FL290" - 200+ miles before economical descent point. So, I start down from FL350 at 500fpm. I politely enquire "Are there any restrictions on the descent?" having not been given any to be met with a gruff and un-neccessary exchange involving the fact that 1500fpm or more was needed. Why not say so? Maastricht are generally pretty good in this respect - far less R/T time. It
should by now, following these two threads, be plain to ATC that in the absence of a published altitude restriction, any
early un-specified descent request WILL, as Javelin says, probably be conducted at 500fpm by most crews to try and protect their fuel reserves. A given rate or a 'level by xxx' will sort it all out.