Analysis of official census figures by Prudential found that three in 10 (30%) people living in Christchurch, which is home to an 11th century castle and a large natural harbour, are retired.
Tower Hamlets in London was found to have the lowest proportion of retirees in the UK, with just one in 16 (6%) of people there who are pensioners.
The proportion of pensioners living in Christchurch is almost double the national average of 16%.
Almost half of homes currently listed for sale in Christchurch have a price tag of at least £300,000, according to property search website Zoopla. Last year, a beach hut in the area sold for £170,000 two days after going on the market.
The South West, with its relatively warm climate, an abundance of beaches and miles of English countryside, was found to be the most popular region for retirees generally. Almost one fifth of people living there are of pension age.
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Wales has the second biggest concentration of pensioners at a regional level, while the North East, the South East and the East Midlands also proved popular.
London, which has seen a particularly strong growth in house prices in recent months, is the least popular region for retirees.
Only around one in nine (11%) people living in the bustling English capital are pensioners. Outside London, Northern Ireland has the lowest concentration of pensioners, at just under 15%.
Vince Smith-Hughes, retirement expert at Prudential, said: "Perhaps unsurprisingly, there's a tendency for people to move out to the country when they stop working, where property prices can be lower and the quality of life is often thought to be higher.
"However, people planning to stop working shouldn't assume that a move to the country is the simple answer to a comfortable retirement, as the cost of living in these hot spots can be surprisingly high."
Here are the percentages of people living in each region who have retired, according to Prudential's findings:
:: South West, 19.6%
:: Wales, 18.4%
:: East, 17.5%
:: North East, 17.3%
:: South East, 17.2%
:: East Midlands, 17.1%
:: West Midlands, 16.9%
:: Scotland, 16.8%
:: North West, 16.6%
:: Yorkshire And the Humber, 16.6%
:: Northern Ireland, 14.6%
:: London, 11.1%
:: UK, 16.4%
And here are the local authority areas with the biggest concentrations of retirees and the percentages of people living there who have retired:
1. Christchurch, Dorset, South West, 29.7%
2. West Somerset, South West, 29.1%
3. North Norfolk, East of England, 28.8%
4. Rother, East Sussex, South East, 28.4%
5. East Devon, South West, 28.2%
6. East Dorset, South West, 27.9%
7. Tendring, Essex, East of England, 27.0%
8. West Dorset, South West, 26.5%
9. Arun South East, West Sussex, 26.3%
10. East Lindsey, Lincolnshire, East Midlands, 26.0%
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