A pressure group has said figures on emigration add weight to its concerns over the level of immigration to the UK.
Sir Andrew Green: Real issue is net migration
Migrationwatch UK called on the government to cut immigration to the same rate as emigration.
Spokesman Sir Andrew Green said emigration figures published by the BBC needed to be seen alongside the net gain from immigration.
Figures from a think tank estimate that 5.5m Britons currently live overseas.
The research, conducted by the Institute for Public Policy Research, predicts that up to one million more Britons will leave in the next five years. It says most those leaving are either young and skilled or the retired.
Figures show that rising immigration over 40 years has largely masked the departure of Britons from the population.
Commenting on the research, Sir Andrew said: "There is no disagreement on the fact that migration is a natural part of an open economy and that it involves flows in many directions as this report clearly demonstrates.
"The real issue is the right scale of immigration into Britain in the present circumstances."
Sir Andrew said that Britain had for centuries been a country of emigration, rather than immigration - something the IPPR's report confirmed. Immigrants only began to outnumber emigrants in the mid 1980s - and since 1997 their numbers had increased very sharply, he said.
"This net migration is the key issue - that is those who come minus those who go," he said.
"We now face by far the largest wave of immigration since 1066, even allowing for those who emigrate. This is putting enormous strain on our infrastructure, public services and on social cohesion.
"Net foreign immigration at 300,000 a year has trebled in the last 10 years and is now three times net British emigration."
Sir Andrew said government figures forecast immigration accounting for 83% of population increases and 31% of household formations.
"Immigration is now adding the equivalent of the entire population of Birmingham every five years," he said.
"Nevertheless, the fact that British emigration has roughly doubled in the last 10 years to about 100,000 a year presents an opportunity.
"If we can cut immigration to about that level we can attract such skills as we need without adding still further to the population of a congested and overcrowded island.
"The real answer to skills shortages lies in training our own work force, not in immigration which can become a disincentive for employers to pay for training."