Heathrow proposes privately-funded M25 tunnel to enable third runway construction

Heathrow Airport unveiled a plan to reroute a portion of the M25 by building a new tunnel and bridges 130 metres west of one outlet motorway, enabling the third runway to be added with minimal disruption to daily traffic. The airport would finance the works privately and switch vehicles onto the new route during carefully scheduled overnight closures, avoiding the prolonged shutdowns seen at the Junction 10 improvement project.

Alternative designs, such as constructing over the M4 spur, were rejected because they would require extensive demolition and cause greater inconvenience for road and rail users. Heathrow points to successful implementations of similar infrastructure at Frankfurt and Paris Charles de Gaulle as evidence of feasibility. The third runway, estimated at £49 billion, is promoted as a catalyst for over 100,000 jobs and £33 billion of private investment, though some MPs dispute the projected economic benefits.