THE Prime Minister has branded migrants' Channel crossings a "very bad and stupid and dangerous and criminal thing to do" as he hinted at changing laws to tackle the crisis.

Boris Johnson's comments came as a French politician warned the UK's decision to send in the Royal Navy "won't change anything" and a former Home Office official said he was sceptical of the plans.

Efforts to address the crisis intensified this morning as more crossings continued, with an inflatable dinghy thought to be carrying more than 20 Syrians met by a Border Force patrol boat off the coast of Dover in Kent.

At the same time, the Royal Air Force (RAF) dispatched a plane to survey the Channel after the flight was authorised by Defence Secretary Ben Wallace.

The Government has faced growing criticism and accusations of being "increasingly chaotic" in its handling of the crisis.

SNP defence spokesman Stewart McDonald commented: "Surveillance flights are supposed to detect and monitor hostile threats, not dinghies filled with desperate human beings who have committed no crime and pose no threat. This appalling display of heavy-handedness is a criminal waste of money and an utterly immoral pursuit."

Amnesty’s Refugee and Migrant Rights programme director Steve Valdez-Symonds has said that Home Secretary Priti Patel’s approach is wrong and dangerous.

He said: “What is needed is co-operation with France to share responsibility for providing a place of safety, including the UK Government reuniting families and enabling more people to travel safely to make asylum claims in this country.

“But while ministers beat their chests, the real and immediate needs of women, men and children fleeing war and persecution are being ignored.”

This morning, speaking during a trip to St Joseph's school in Upminster, Johnson said: "There's no doubt that it would be helpful if we could work with our French friends to stop them (migrants) getting over the Channel.

"Be in no doubt what's going on is the activity of cruel and criminal gangs who are risking the lives of these people taking them across the Channel, a pretty dangerous stretch of water in potentially unseaworthy vessels.

"We want to stop that, working with the French, make sure that they understand that this isn't a good idea, this is a very bad and stupid and dangerous and criminal thing to do.

"But then there's a second thing we've got to do and that is to look at the legal framework that we have that means that when people do get here, it is very, very difficult to then send them away again even though blatantly they've come here illegally."

READ MORE: Priti Patel warned using Navy to block asylum seekers ‘unlawful’

Meanwhile Calais MP Pierre-Henri Dumont, when asked about involving the Navy, told BBC Radio 4's Today programme: "This is a political measure to show some kind of resource to fight against smugglers and illegal crossings in the Channel, but technically speaking that won't change anything."

Asked if it might be a deterrent, he added: "Yes, but that's dangerous, because if there is a vessel from the Royal Navy trying to push a vessel, very small boat full with migrants, back into French waters - first you could say that you've got British vessels entering French waters, I don't know if the British Government would be very happy to see the other way, if French vessels would enter without any ask, before or without any decision before, into British waters."

He said French authorities were already trying to do "whatever we can" to intercept crossings.

Regarding speculation the UK may need to provide an extra £30 million to help the French fund patrols, he said: "Well, if it takes money to help the French increase their resources and their manpower then that will have to be done. There's a long history of Britain putting money into resources for the French on the French coast."

More than 4000 migrants have now reached the UK so far this year, making the dangerous crossing across the world's busiest shipping lane.

At least 597 arrived in the country in a surge of crossings between Thursday and Sunday.

The Home Office has now appointed a former Royal Marine to head up an operation to tackle the problem and formally requested help from the Royal Navy for help - a move branded a "completely potty" idea by a Ministry of Defence (MoD) source.