It looks like the document has been moved. I found it at
http://www.ais.org.uk/uk_aip/aip/pdf/ad/30101.pdf section 3.3.2
It states:-
Pilots with a valid IMC/Instrument Weather Rating are recommended to add 200 ft to the Instrument Rated pilots' DH/MDH, but with absolute minima of 500 ft for a precision approach and 600 ft for a non-precision approach.
Now, the question is, what is recommended? I think it can be argued that everything after the 'recommended' is just that - i.e., it is only recommended that the absolute minima is 500/600 ft. If it is mandatory, then why wasn't it written:-
Pilots with a valid IMC/Instrument Weather Rating have an absolute minima of 500 ft for a precision approach and 600 ft for a non-precision approach and are recommended to add 200 ft to the Instrument Rated pilots' DH/MDH?
However, perhaps the point is that to get this low you must be current at getting this low. Certainly when I did my IMC and subsequent renewals, my decision height was based on this recommendation.