I think you mean 1000 AGL (or above highest obstacle in vicinity
Just realised that if not descending below 1000ft above the highest obstacle within 5 nm of track means not descending below approx 1500ft (or higher) in my part of the London TMA
Example - Planned descent to 1000ft, ATC advises Tower 3nm ahead of track up to 750 agl (which you know about and have planned for) - although
you are navigating clear of the tower you will now need to maintain 1000 ft above that tower to remain legal in IMC (Not below 1000ft above the highest point within 5nm). So you cannot now descend below 1,000 + 750 + elevation at tower (lets say 2000 ft)
I realise in hindsight that my descent to 1000 ft to break cloud "near" the tower (even though there was awhopping great VOR prior to twr which was my turning point) was technically
illegal.
Lesson learned (measure 5nm each side of intended track and be more conservative with min descents, this will ensure that you remain legal and safe but will require more planning as you now need to ensure that you can break cloud prior to destination and any obstructions on route will keep you high