Through Beijing back to Uk

I am a British citizen and will be travelling through Beijing on a flight from Kuala Lumpur to the UK. I will be in Beijing under 72 hours. My flights are with two separate companies however (one with air asia rom kuala lumpur to Beijing and then with Finnair from Beijing to UK). Will I need a visa to exit the airport or will the transit visa cover me if I have proof of UK citizenship and an onward ticket?