Sky News Reports The interception, one of the biggest this year, took place in bad weather and the migrants were found hidden beneath the deck.
A fishing vessel with 69 migrants hidden on board has been intercepted by UK Border Force boats off the Norfolk coast and escorted into Harwich.
The migrants, all Albanians, were being questioned about alleged immigration offences.
The National Crime Agency (NCA) also arrested the vessel’s three crew members – two Ukrainians and a Latvian.
They were being questioned on suspicion of facilitating illegal immigration.
The interception off Great Yarmouth, one of the biggest this year, was carried out in bad weather and the migrants were found hidden beneath the deck.
The 30-metre boat had sailed the night before from Ostend in Belgium and was intercepted off Great Yarmouth, Norfolk.
NCA deputy director of investigations Craig Naylor said: “This was clearly a significant incident and a significant attempt to breach the UK’s border controls.
“Our investigation into this attempt continues, and I’d like to thank our partners at Essex Police, Border Force and Immigration Enforcement for all they did last night and their ongoing work in support of our investigation going forward.
“Working with our partners we are determined to do all we can to disrupt and dismantle people-smuggling networks, and prevent them from exploiting migrants for profit.
“Our aim is to target those who cause harm, safeguard those who are most vulnerable while securing the United Kingdom’s borders.”
The interception was part of a joint operation between the NCA, Immigration Enforcement and Border Force.
Home Secretary Priti Patel said: “I’ve been clear that I’ll use every arm of the law to break up the ruthless gangs who facilitate this criminal activity.
“Yesterday’s operation was a big win for our intelligence and law enforcement agencies who have halted a serious illegal enterprise and cut off a source of funding for an organised criminal gang.
“We are unapologetically returning migrants who have no right to stay in the UK to safe countries with flights every week and will do whatever we can to make this route unviable.
“My thanks go to all our operational partners for their role in the important criminal investigation.”