The number of Spaniards moving to the UK has soared over the last four years by 117% taking the number from 63,000 to 137,000.
During the period, the number of Portuguese trying their luck in the UK jumped from 96,000 to 140,000, according to Migration Observatory.
The changes have made Spaniards the third largest group of Europeans in the UK after those from Poland (818,000 last year) and Romania (223,000).
Portuguese are the sixth largest group after Italians (176,000) and Hungarians (96,000).
Taken together, Portuguese, Spaniards and Italians accounted for 24% of new arrivals during the 2011 to 2015 period, while 49% were from Poland and Romania.
Nearly 3.3 million people from European countries are now living in the UK.
"The UK has been outperforming the rest of Europe for quite some time. Employment is at a record high and the number of people in work is the highest it has ever been," Robert McNeil from the Migration Observatory said
"With job creation comes the demand to fill these jobs. The majority of those filled by migrant workers are unskilled and fairly low wages and don’t have a huge amount of competition from UK-born workers.
"They tend to be short-term, low wage jobs in the industries of hospitality, agriculture and construction.
"In terms of Spanish workers they are drawn to hospitality jobs working in cafes, restaurants and hotels.
"We wouldn’t expect the high level of youth unemployment in Spain to last forever and therefore in time there will be less incentive for those people to leave Spain and work elsewhere."
And, according to the agency, the pull to Britain was for jobs rather than benefits.
"While certainly there will be some EU migrants claiming jobseekers allowance, we are talking about a very low percentage, that is certainly not a major factor," explained McNeil. "The percentage is lower than that of the British workforce.
"It may be that in terms of other benefits, namely tax credits, the percentage is higher but that is because we are talking about a group who largely exist in the low wage bracket where these benefits are available."
