Boris Johnson has written to Emmanuel Macron, formally proposing combined patrols on French beaches as soon as next week to halt tiny boats carrying migrants on route to the United Kingdom.

The prime minister also called for a new "returns agreement" between the two countries in a letter outlining UK preparations after 27 people perished in the English Channel.

If Paris approves the plan, migrants who unlawfully enter the UK will be returned back to France, with London taking in more child migrants with British family ties in exchange.

The partnership, according to Downing Street, is the greatest long-term answer to the rising problem of boat crossings because it would put smugglers who promise a passage into the UK out of business.