HZMIS.... what's a "VOR departure"? I've never heard that term. 2 miles DME is not quite the same as 2 miles from Heathrow as the VOR/DME is north of Heathrow. That particular procedure has been standard for some time for traffic departing 09R and turning to the west. The actual heading after the turn will vary as it is assigned by the radar controller immediately prior to departure and takes into account inbound traffic downwind for 09L. Some SIDs use the London VOR/DME and others use the ILS DME to determine turning points. Outbounds restricted to 4000 ft sounds like a temporary measure - maybe a photo survey aircraft or many other possibilities.