Uh.. was that an unknown, before? They don't actually know for sure if they can track and intercept Russian air force? Cameron doesn't sound very informed, about his own military. I find that odd.
RAF jets scrambled after Russian bombers seen off Cornwall
http://www.bbc.com/news/uk-31530840
British radio hobbyist picks up Russian bomber transmission, in Russian, in code over the Cornwall coast:
This is the terrifying sound of a Russian bomber sending coded messages back to base – as it flies near CORNWALL.
https://www.youtube.com/watch?v=Bo0i8Wr9rz4
Eyewitnesses claim the bomber flew into UK airspace, because they SAW it inland, contrary to Cameron's assertion that the bomber never crossed UK airspace:
Russian bomber flew inland over Cornwall, witness claims
“We were in St Eval when we saw a big black plane that looked like a tank. We thought: where’s that going? It was going along [the route of] the A30,” she said. “As we drove on the big black plane came back again. As Claire [Bamford’s driving instructor] took over to drive back we saw a silver plane, which was the Bear bomber. It’s travelling at the bottom of the St Mawgan valley so we can see it’s not out to sea, it’s in the valley. It’s long and thin, it’s got swept-back wings.”
http://www.theguardian.com/uk-news/2015/feb/19/russian-bomber-flew-inland-cornwall-uk-airspace-witness
Let me repeat that:
**** it’s not out to sea, it’s in the valley. It’s long and thin, it’s got swept-back wings. ****
"In the valley" is most certainly within British airspace, whether the prime minister dignifies that with an acknowledgement, or not.