I'm not sure that the free CAA data gives the numbers for Int-Int connections. Table 1 of the summary of the 2012 survey (see
http://www.caa.co.uk/docs/81/2012CAAPaxSurveyReport.pdf) shows that an estimated 262,000 of MAN's departing pax in 2012 were making connections to an International destination. And 167,000 were making connections to a a Domestic destination.
Presumably the number of pax connecting Int-Int would be substantially less than the 262,000, as I imagine that a lot of these pax are connecting off Domestic flights (eg FlyBe).
Not a complete answer by any means but I hope it helps.