The drive was to take us along the southern Florida archipelago, where we were to dive among tropical fish and swim alongside dolphins. We’d spent the afternoon at the Venetian Pool, a splendidly grandiose but muted folly, in Coral Gables, Miami. It’s the city’s most sprauncy district, with the most expensive property, the most teasy-weasied lawns and highest per capita income.

Like so many British visitors, I decided to hire a convertible, and we were soon on our way, burning up cheap petrol across Biscayne Bay to Highway One, the 150 miles of road that stretches all the way from the mangrove swamps of southern Miami to the tip of the archipelago.

The Keys are simultaneously beautiful and raw. They form an idyllic vacation-land that remains curiously blue-collar in attitude. Don’t expect pristine beaches and fawning locals; many of the developments along Highway One are as down-to-earth as they come.

But it’s still possible to find all kinds of accommodation, from resort complexes to roach motels, and virtually any sort of food – including alligators, which have their own ideas about lunch. If you see one, it’s best not to get out of the car.

The first key of any significance is Key Largo, the setting for the Bogart-Bacall classic of 1948. It’s a sprawling, everyday kind of town, its name more evocative than the experience it offers, but justifiably renowned for the quality of its diving. If you come here, you must at the very least take a trip out on a snorkel boat to the coral reef.

A string of smaller keys link the Upper Keys to the Middle Keys. We stopped off for a conch-fritter lunch at Islamorada; most of the roadside restaurants offer excellent seafood plucked from the Gulf of Mexico and the Florida Straits.

The Middle Keys, where we were headed, are probably the least visited of all the settlements along the archipelago. Yet they are home to the Dolphin Research Center, a pioneering non-profit organisation that specialises in resettling dolphins that have been abused in theme parks or suffered injury or bereavement in the wild.

If you book in advance (at least 30 days ahead) it is possible to swim with the dolphins or enjoy a 20-minute “splash session” with them. The dolphins jump, play and even kiss on demand; it seems they are enjoying themselves too. My own children were enraptured by Kibby, a bottlenose refugee from a Mexican theme park, who was playful and entertaining, and clearly enjoyed being spoilt by visitors and staff.

Key West, at the very tip of the archipelago, is about 90 minutes from the Research Center. The drive takes you across Seven Mile bridge, a favourite of long-distance runners, fishermen and seagulls.

Once in Key West, most of the important landmarks – Hemingway’s house, Bahama Village – are best approached on foot. But forget about getting to any of the Keys without a car, and allow four hours for the trip, longer if your visit coincides, as ours did, with a special event such as the Key West Drag Race – not cars, but female impersonators.

How to get there

Mark Edmonds travelled to the Florida Keys with Jetsave Florida, tel: 0871 231 2271; www.jetsave.co.uk . Prices start from £2,199 for a family of four for seven days

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