London — Residents in the city of Deal complained last year about noisy motor boats allegedly dropping off migrants at night after crossing the English Channel. But authorities reacted with disbelief.

Then in April, the British coastguard rescued two Iranians who were trying to cross the channel, which separates Britain and France and connects the North Sea with the Atlantic Ocean. Authorities still considered it an isolated incident.

But officials now seem worried. The coastguard discovered 18 Albanian migrants in two inflatable boats on Saturday night in the most significant rescue operation yet, raising fears that an increasing number of migrants might be risking the dangerous journey across the channel by boat. Two British smugglers were arrested.

“It’s starting to become a very similar situation to that seen in the Mediterranean,” Bernard Barron, the president of France’s coastguard, said after the rescue. “My biggest fear is that the same kind of tragedies we see in Greece or Italy will start to repeat in the channel.”

The English Channel is the world’s busiest shipping lane, but its unpredictable currents can be extremely dangerous for smaller boats.

Most migrants who try to reach Britain jump on trucks entering the channel tunnel or hide in large container vessels. But as surveillance of major container ports and the tunnel has increased, officials say more migrants will pay to be smuggled despite the risks.

Britain’s National Crime Agency has warned that smugglers now demand less than $200 per migrant for the 21-mile boat trip. The lower prices could lure even more migrants onto such vulnerable vessels that have so far mainly been associated with tragedies in the Mediterranean.

Whether or not official numbers on prices and arrivals are reliable, however, remains questionable: Former top officials have publicly acknowledged that border agencies have so far failed to assess the real extent of the influx over the channel.

“We just don’t know the extent of this,” John Vine, a former chief inspector of borders and immigration, said in an interview with the BBC.

“But I think it is reasonable to assume that this is something that might have been happening, and if this is now the start of a new trend, we certainly need to gather the intelligence and the resources to nip it in the bud,” Vine was quoted as saying.

Asked about the issue in April after the two Iranians were rescued, an unidentified spokesperson for the British Home Office explained in an email: “Border Force uses a combination of cutters, radar and aerial surveillance to detect and stop small craft.”

“We also work closely with domestic and international partners on an intelligence-led approach to identify unlawful maritime activity including facilitation and clandestine entry,” the spokesperson explained.

In Deal, residents said in April they had known for years that migrants were arriving by speedboat.

One fisherman who spoke on the condition of anonymity said that about a year ago, several men asked him whether he wanted to earn money by smuggling refugees across the channel — an offer he said he declined.

“They asked me how long it would take to cross the channel — not with drugs, not with cigarettes, but with people,” the fisherman recalled.

He says crossing the channel in a fishing boat can easily become dangerous because of unpredictable weather, currents or cargo ship traffic.

But such boats would still be far safer than the inflatables and dinghies that now are being used for the potentially deadly journey.