There is in fact a publication in the UK that covers this: "Noise from Arriving Aircraft" published by NATS, BAA and others, which is primarily aimed at LHR, LGW and STN (but not RW05)
It does, on page 8, mention a 2.5NM level segment to decelerate (therefore the assumption is that thrust is at flight idle) before the descent commences. Furthermore there are very good tables on page 15 which give you V/S and FPA versus distance and altitude. These tables also mention the level segment - but assume 20secs of level flight at 210KIAS - one can only assume that the 2.5NM previously stated is a maximum (ICAO requires a minimum of 1.5NM)
I'm with Rainboe on the FMS/FMC/FMGC. On my type, it will schedule the next flap manoeuvring speed before you've wound 'em out which could be a tad embarrasing if you get distracted!