At around 7am, Border Force agents received notification of six men and an inflatable boat on a beach in Kingsdown, Kent.
It appeared the dinghy had been left on the beach overnight, dumped alongside life-jackets and canisters of fuel.
Two men identifying themselves as migrants were detained at Folkestone police station and later transferred to immigration officials.
Meanwhile, at 9.30am Border Force agents intercepted a dinghy containing suspected migrants off the coast of Dover and towed it to shore.
Officials were seen helping the suspected migrants disembark and wrapping them in blankets.
In all, at least a dozen of the 18 men who arrived in the UK identified as Iranian, while at least one said they were Iraqi.
It comes amid a spike in the number of migrants risking their lives to cross the English Channel from France, despite government attempts to discourage people from trying to make the journey.
Following several incidents over Christmas, Home Secretary Sajid Javid – who has questioned whether those trying to cross the Channel are “genuine” asylum seekers – redeployed two Border Force cutters from the Mediterranean.
Mr Javid declared a “major incident” following the December uptick, with 80% of the 539 migrants who attempted to travel to the UK on small boats in 2018 having done so in the final three months of the year.
The Channel is one of the busiest stretches of water in the world, but – despite the dangers it poses – migrants remain determined to cross it as it has become increasingly difficult for them to get to the UK by lorry or train.
Elsewhere, up to 170 migrants are feared dead after two accidents in which dinghies sank in the Mediterranean after leaving North Africa for Europe.
One of the vessels capsized off Libya after departing the country on Thursday, prompting the Italian navy to stage a rescue operation, while the other went missing after a collision near Morocco.
Just three out of the 117 people aboard the boat that left Libya have been rescued alive, and there were 53 on the dinghy that departed Morocco.
The numbers of dead from the two incidents are yet to be verified by the United Nations Refugee Agency, but it said in a statement that it was “deeply saddened” by the estimated figures.