Traité de Cantorbéry) was signed by British Prime Minister Margaret Thatcher, British Foreign Secretary Sir Geoffrey Howe, French President François Mitterrand and French Minister of Foreign Affairs Roland Dumas on 12 February 1986.

[1][2][3] The treaty is significant and unusual because it is a modern and recent modification to the national borders of the UK and France.

The treaty prepared the concession for the construction and operation of the "fixed link" by privately owned companies.

The appendices to the agreement cover specific aspects, including the purchase and sale of land, insurance obligations and the exercise of the right of substitution.

The right of substitution provides for the temporary transfer of operation to two entities under the control of the lenders that financed the tunnel to allow them to be reimbursed.