Six lines cross over six at Kenton/Northwick Park; the only other location in London where a comparable number of lines cross over another railway is near West Ruislip, where 8 lines (3 at Ruislip Depot, the 2 tracks of the Central line, and 3 on the Chiltern) cross the Met/Picc.
(Correction: last time I referred to the Kenton/Northwick Park location, I spoke of four lines over four. That was clearly incorrect—does this require an adjudication?)