So NFR, when I'm vectoring to the ILS at LHR with traffic at 4,000ft and I say "turn right heading 240 degrees, cleared ILS approach 27R" can you guarantee me that the traffic won't then descend to 2,500ft which is the stated start altitude on the approach plate for a radar vectored ILS/DME approach to 27R.
It would be just a little embarrassing if traffic did descend in such manner, collecting as it would other IFR and VFR traffic below it.