There seems to be some conflicting info being offered here. On re-reading I can see where some of this at least has come from.
When in the UK and being radar vectored for an ILS approach, which on the ILS approach chart has a procedural ILS depicted, you do not have to descend to the published platform once cleared to descend on the glideslope. Even if you were flying the procedural ILS, unless it depicts a platform altitude that you have to be 'at', you can fly a constant descent to only actually pass this altitude as you capture the glideslope.
However, and this is something we regularly experience in places like Spain, you will often fly an approach procedure from the Initial Approach Fix (Alicante springs to mind), when you are descending to a flight level, under radar, and then they clear you for the approach. This is the last they say to you until they hand you over to the Tower frq. In this scenario you descend in accordance with the procedure without further prompting, obeying the various altitude restrictions depicted on the chart until you are fully established on the ILS.
I believe that the UK system of controllers asking you to report established on the localiser before being cleared to descend with the glideslope came from places like Heathrow where controllers would clear a/c from a long way out for the ILS and some pilots were then interpreting this to mean they could descend to the platform altitude depicted on their charts. This led to many a/c descending to the platform (something like 3000'?) at considerable distances out (like 20nm) and then overflying London!
I personally do not see how you can descend to the platform unless you are either;
a. On the published procedure. or
b. Under radar control with a radar minimums chart available to you.
Otherwise you need to stay at your (radar vectored) cleared altitude or MSA until you establish on the localiser (which incidently is at half scale deflection, not "needle alive") and then capture the glideslope.
PP