The Treaty of Hampton Court (20 September 1562) saw Elizabeth I of England agree to provide support for the Huguenot cause in France during the First War of Religion, but the alliance produced very little practical aid for the Huguenots.
The Huguenot leaders had been reluctant to turn to foreign powers for aid until it became clear that the Catholics were negotiating with the Spanish. At that point they sent representatives to England, where they found Elizabeth ready to offer limited assistance but at a heavy price.
Elizabeth's main interest was the recovery of Calais. The last English foothold in France had fallen to a surprise attack in January 1558, during the last of a long series of Hapsburg-Valois Wars. The war had been ended by the Treaty of Catteau-Cambresis (3 April 1559), which had included a agreement to return Calais to the English after eight years, as long as the English didn’t interfere in France or Scotland.
Elizabeth agreed to provide the Huguenots with a loan of 140,000 men in return for an agreement that Calais would be returned to England once the Huguenots had won the War of Religion. Dieppe and Le Havre would be occupied by English garrisons of 3,000 men, officially to protect them against the Catholics, but actually as a security for the eventual return of Calais.
The treaty had a very limited impact on the fighting in France. The earl of Warwick led a garrison into Le Havre, but made very little effort to help the Huguenots further in France. When the First War of Religion came to an end in 1563 the English were exposed to attack by a united French army and after a short siege Le Havre was reoccupied by the French on 1 August 1563.