Video report by ITV News Correspondent Angus Walker
A bag is left on the beach which once contained an inflatable boat, after nine migrants used the dinghy to help them cross the Channel.
ITV News saw the boat setting off and notified the French authorities on Wednesday morning.
The nine individuals, including eight Iranians and an Afghan, were rescued by the UK Border Agency.
Thermal imaging filmed by ITV News has captured the moment nine men set off from Calais to cross the English channel
They were reported to French authorities shortly after the boat set off but it was not until they were in British waters that they were detained.
Their journey also prompts questions about the efforts Europe is taking to stop illegal immigration.
The Home Office Minister for Immigration said she had "seen no evidence of the French being willfully slow, I have seen the French being absolutely determined to put safety first as they rightly should do."
Caroline Nokes added: "And this is a tiny tiny craft which is impossible for people to board safely and I think we have to reflect on that, is that safety in these instances must always come first."
The French coastguard admitted on Thursday they only had one boat on operational duty the night ITV News saw the migrants crossing.
Lieutenant Ingrid Parrot, of the French Coastguard said: "When we have the information of a crossing, sometimes we are both near so it is easy because our boats, just take the dinghy and the migrants and go back to France, but sometimes we are not near."
Dover MP Charlie Elphicke said the report from ITV News was extremely concerning and the French need to "do their bit".
The Tory MP said: "We need to see the French do their bit, they've been paid millions of pounds from the British tax payer under the action plan that was agreed last month, to make sure sure they patrol their beaches and their coastguards intervene."
ITV News was able to report the dinghy first taking off through a hidden camera.