Thanks again, LV2TNDM
I'm currently running Schwalbe Marathon 35's at about 80-85psi (85 being the max). I reckon I could bring this down a tiny bit for comfort, but London roads do can induce snake bites quite frequently.
I'm confident that taking a wire brush and isopropyl to the rims has solved the issue. Probably about 35 miles without an issue anyway.