"Spec Area" is now R160 and it covers bits of both Heathrow Class A and City Class D.
Within that are 3 Restricteds with tops at 1400ft : R157, 158, 159. They pretty much nuzzle up to each other. So (unless you have an ENSF) you will have to remain above 1400ft.
This will assist:
http://www.ais.org.uk/aes/pubs/aip/p...s/32LL0302.PDF