That is what Australia did. Like our current policy, they tried paying Indonesia to stop the boats and they weren’t doing it because it’s not in their interest to. So they started turning boats back and escorted them all the way to Indonesia.
It caused a diplomatic ruckus and no doubt this policy would. Ultimately, the UK has a right to defend its territory.
It is practical, there’s a blueprint in place and we’re not the only country to has experienced an asylum crisis via small boats.
Australia’s policy was successful. Paying the French, ‘1 in, 1 out’, ‘safe and legal routes’ do not stop the issue.
If the French want to play ping pong with migrant boats in the Channel, so be it. France will never stop 30-50k refugees leaving their shores every year if they know Britain will pick the tab.