I thought Air China minimum connection time at PEK for Intl-to-intl transit is 60 minutes. Which would make this a non-legal connection that needs to be fixed before your journey starts. Call CA and point this out, as it would be better to get rebooked on a different sequence now. If you want to risk these particular flights, assume you'll misconnect and the rebooking might cause you to get to London a day later than you planned....so have some flexibility on your UK arrival end.