RMC, you are correct, the level restriction does still apply when put on a heading. People are getting confused by being cleared to a point beyond one with a restriction where the level by clearance does need reiterating if still required, but not for the case of headings.
Level By means exactly that - level by, so you can descend at maximum rate from the moment the clearance has been read back, or stay high and descend at the last minute, and everything inbetween, the choice is yours. As long as you are level by the time you cross the point, that is all that matters. If you are having difficulty in complying then aiming for a safer 5nm before the point works, and asking for either a distance or time from London Area ATC doesn't cause too much extra hassle, the computer can work it out very quickly and simply.
Fly in France.
From my experience they nearly always give a rate of descent to fly which will get us level at the waypoint eg FL220 at Anglo or FL190 at Ratuk.
...and both of those restrictions are often missed as a result. It doesn't work, but being told to be level by does. It baffles the receiving London sectors why the reluctance for France to use Level By restrictions.