At a press conference at Sandhurst, Theresa May and President Emmanuel Macron spoke about their strategy to "improve the security of the continent".
This was President Macron's first official visit to the UK since taking office last May.
Mrs May said the UK-France combined joint expeditionary force would be ready to deploy up to 10,000 troops
"quickly and effectively to face any threat"
The Prime Minister also confirmed the UK had agreed to step up support for French operations against Islamist terror groups in the Sahel region of northern France.
Three UK Chinook helicopters and their crews will be deployed to the area and Britain will continue to provide heavy-lift aircraft.
Other areas discussed were that France will commit troops to a UK-led battle group deterring Russian aggression in Estonia.
Mr Marcon echoed many of Theresa May's statements.
The French President said France's defence and security co-operation with the UK had not been
"challenged or revisited or impacted"
by the vote for Brexit.
Mr Macron also said that Britain's offer of military assets in the Sahel was "a very important commitment and contribution ... a strong token of your commitment and our joint willingness to work together and fight together for security".