First unveiled in 1966 as part of the Greater London Council's new "London Motorway Box" proposal, the North Cross Route was to form the northern flank of London's innermost motorway ring road.

The GLC considered it one of the most urgently required new roads and it progressed further through the planning process than most of their other road proposals. In August 1966, the consultants Travers-Morgan published the North Cross Route Engineering Report, which set out firm proposals for the motorway — a route, a design specification, junction layouts and a full set of engineering plans. This means that (quite unusually) we have a very clear picture of how the North Cross Route was meant to look.

The road itself would have had four lanes in each direction, with hard shoulders on both sides of both carriageways, and extra parallel carriageways running alongside in some places. Parts would have been elevated and others sunk below ground level, and in more than one place its connections to surrounding roads called for junctions with multiple flyovers stacked above one another and double-deck viaducts.

The motorway would have sliced through Harlesden, Kilburn, West Hampstead, Camden Town, Islington, Dalston and Hackney. A motorway through these places would be unthinkable today, but most of the areas affected by the North Cross Route were relatively deprived in the 1960s, and few were as popular or wealthy as they are today.

It was never going to be easy, however, to drive a motorway through Hampstead or Belsize Park. The plan would have ruined the leafy, wealthy character of the area by carving a cut-and-cover tunnel through it. This would also have involved the demolition of Sigmund Freud's house on Maresfield Gardens (now the Freud Museum). An alternative proposal, avoiding Belsize Park by boring four two-lane tunnels, was rejected on grounds of cost.