The government's scheme for offering an estimated 3.8 million EU nationals the right to live permanently in Britain after Brexit has been riddled with controversy.
Responding to a public outcry, Prime Minister Theresa May in January scrapped a 65-pound ($82) fee that would have been imposed had a so-called "no-deal Brexit" gone into effect.
The program's status has been weighed further by uncertainties over when — or even if — Britain pulls out of the EU.
The U.K. interior ministry said 103,0000 Polish citizens had applied for permanent residence in the first four months of the year.
Romanians filed 90,000 applications and Italians 71,000, the figures showed. Portugal and Spain rounded out the top five.
The scheme is being overseen by Home Secretary Sajid Javid, who is one of 11 declared candidates in the race to succeed May as government chief in July.
"EU citizens are our friends, neighbors and colleagues who contribute so much to this country. Whatever the outcome of Brexit we want them to stay," Javid said in a statement.
"Our free and straightforward EU Settlement Scheme has already seen 750,000 applications - which is immensely encouraging. I hope this early success continues in the coming months."
Economic worries and a desire to limit migration — particularly from eastern European countries such as Poland and Romania — was one of the factors that pushed voters to back Brexit in 2016.
Britain's split from the other 27 EU nations, originally scheduled for March 29, was delayed until April 12 then postponed until October 31 due to the U.K. parliament's refusal to approve the sides' separation terms.
London may still ask Brussels to grant it another extension, or decide to walk away without a deal — an option that businesses worry would lead to chaos at the border and across the broader economy.