About 230 migrants tried to sail to England from northern France in December, according to the UK government.
Officials warned smugglers ”with a complete lack of regard for human life” were planning to send more migrants across the water on dinghies.
Sporadic crossings have been seen since the start of the Mediterranean refugee crisis in 2014, but numbers in the Channel started to increase in November.
A group of 12 Iranian migrants, including one child, were the latest detained by UK police after landing on a beach at Lydd-on-Sea, Kent, on Monday.
Investigators believe that increased security in Calais, where migrants have previously boarded lorries through the Channel Tunnel, and other French ports may have contributed to the spike in dinghy crossings.
Two Border Force cutters are to be called back from abroad to join a third already patrolling the Channel.
But lawyers and campaigners have cautioned that the recent rise has been “blown out of proportion” as the numbers arriving constitute a “tiny proportion” of people coming to Britain to seek asylum.
Government figures show there were an estimated 1,832 clandestine entries to the UK south coast ports – including people arriving on small boats as well as in ferries and in the back of lorries – in 2017/18. This was a decrease of 23 per cent on the previous year, when it stood at 2,366.