For an English person to hook up with a non-English person; especially when a British man seduces a woman from another part of the BritishCommonwealth (e.g. Canada, Australia, New Zealand).
"The plan is to colonise some Aussie tourists soon, 'cos I haven't been laid in ages!"
(Typically) Consensual anal sex between two parties that achieves deep, unprotected penetration with the aim of filling one (or both) party's colon with rich seminal fluid.
Guy 1: Hey, where's that £6.25you owe me?
Guy 2: I'll get it, I swear.
Guy 1: You better, or you'd best start preparing yourself for colon colonisation.