Piccadilly line
In preparation for the Victoria line, cross-platform interchange was to be provided at a few stations, which included Finsbury Park on the Piccadilly line. This meant that the Piccadilly line had to be realigned there, and the Northern City line platforms, being parallel to the existing Piccadilly line platforms, were to be transferred to the pair of lines. The Northern City line would be redirected to the surface platforms. The westbound Piccadilly line track would be rerouted onto one of these platforms, with the southbound Victoria line using the other. The northbound Victoria line would reuse the old westbound Piccadilly line platform and a part of the old tunnels, with the Piccadilly line diversion tunnels spanning .