The warning was meant for British parliamentarians, of course, but MI5 and the government are also trying to send a signal to China. We know what you are doing, and in ministers' words today we "won't stand for it". But in the wake of the collapsed China spying case last month, the security services also want to reestablish a badly dented sense of deterrence. Politics latest: China responds to MI5's spy warning to MPs Please use Chrome browser for a more accessible video player 2:01 Security