Video report from ITV News Political Correspondent Libby Wiener
Boris Johnson is backing a new pressure group aimed at ensuring Prime Minister Theresa May delivers on her promise that "Brexit means Brexit".
In a potentially confrontational move, the foreign secretary has helped launch the Change Britain campaign, which says it will push the government to "deliver the UK’s referendum result in the most effective way".
The organisation is led by Mr Johnson's former Vote Leave colleague, Labour MP Gisela Stuart, and brings together many of those who headed the Leave campaign, including former justice secretary Michael Gove.
In a video message supporting the group, Mr Johnson said that Leave voters and Remain voters must work together to "seize the opportunities that this country now has to forge a positive and exciting new relationship, not just with the European Union, but also with the rest of the world".
Differences over Brexit have already created tensions in Ms May's Cabinet, in particular over whether Britain remains in the single market.
Mr Johnson, who was a leading light in the Leave Campaign ahead of the referendum, has already had his call for an Australian-style points-based immigration system dismissed by the prime minister.
Meanwhile, Number 10 has distanced itself from comments made by another Leave campaigner, international trade secretary Liam Fox, that British executives were more interested in playing golf than exporting goods and services to foreign markets.