Descend to MSA when "cleared approach"

[Checkboard]

In the UK, the Manual of Air Traffic Services (CAP 493), says:

The controller shall use one of the following techniques when issuing a clearance to the pilot to descend on the ILS/MLS glidepath:

•  
  • (1) Clear the pilot for the ILS/MLS approach only if a descent instruction has been issued to the level published in the ILS/MLS instrument approach procedure at the final approach fix, or to a lower level permitted by the aerodrome’s SMAC; or
  • (2) Issue a conditional clearance to the pilot to descend on the ILS/MLS glidepath once established on the localiser; or
  • (3) When it is necessary to ensure that an aircraft joining the ILS/MLS does not commence descent until specifically cleared, solely instruct the pilot to report established on the localiser and to maintain the previously assigned level. Subsequently, the pilot shall either be cleared to descend on the glidepath or given appropriate alternative level instructions.

So you should (in the UK) never be given "Cleared Approach", unless you have also been cleared to descend to the platform altitude (precisely due to this confusion). You should (in your example), if you are cleared to descend to 4000' and intercepting an approach with a 3000' platform, be cleared "once established, descend with the glide". In other words - the 4000' is limiting until conducting the approach - i.e. on the glidepath.

This is because the approaches are surveyed with regard to terrain clearance, but not necessarily airspace. You may thus have a 2500' platform shown on the plate, but the lower limit of controlled airspace is 3000' and VFR traffic may be transiting under arriving traffic at 2500' outside controlled airspace.