Ah, there it is. Listed as a legal connection. I've done 70 minute connections at HKG, and you should have no problem making this, including checked bags. CX desk at LHR will probably issue your boarding pass for 703, in which case, don't waste time at the connections desk at HKG, as you don't need to stop there if you already have a boarding pass for the onward flight. Just go through security back into the terminal, find your gate, and go there directly.