AIP Aerodromes Section 1.1.2 Aerdrome Operating Minima Item 3.3.3 contains the relevant text.
http://www.ais.org.uk/uk_aip/pdf/ad/30101.pdf
although it 'recomends' adding 200ft to the IR DH the absolute minima is still 500/600ft. Earlier on in the document, calculated minima are said to be mandatory.