With over 1,000 islands dotting its coastline, our kingdom is home to a whole lot more sea-surrounded spots than you've probably realised. From 19th-century forts to natural marine reserves, take a look at the British Isles you never knew existed.
1. Eilean Donan, Scotland
Secreted away in the western Highlands, this small tidal island can be found at the meeting point of Lochs Duich, Long and Alsh. Its main feature is a stunning mid-13th century castle, whose tours provide a glimpse into the area's history of family feuds and Jacobite uprisings. There's even a quaint holiday cottage which sleeps four and offers a great base from which to explore the rest of the Highlands.
2. Lundy, England
Lying approximately 12 miles off the coast of Devon, Lundy is home to England's only marine nature reserve. No one bothers with cars here, your own two feet will be plenty enough to discover the village and its 13th century castle, whilst a wetsuit and a fearless approach to English sea temperatures will suffice for taking advantage of the island's superb diving and snorkelling safaris.
3. Piel Island, England
You'll be assured of a royal welcome on this particular Cumbrian outcrop. Piel Island may only be 50 acres and home to no more than a castle, a couple of houses and a pub, but the pub's owners are the King and Queen of their own little kingdom (really, the landlord's official title is King of Piel). You can pitch up a tent just about anywhere for just £5 a night, or snuggle up away from the elements in the Ship Inn's comfortable rooms.
4. Isle of Bute, Scotland
It used to be one of the most popular holiday destinations in Victorian England, but this Scottish isle in the Firth of Clyde has long since fallen into obscurity. So much the better, for the island lives out its days to the sleepy rhythm of the tides an easy 33 miles from Glasgow. Trek the beaches, visit its gothic stately home, take a wee kayak out onto the water and don't miss the fantastic Bute Jazz Festival which takes place annually in May.
5. Jura, Scotland
This is a Rock and Roll island if ever there was one. Famed for its whiskey distillery, Jura was George Orwell's island of choice for writing his classic 1984 and also the spot where British Acid House band KLF decided to burn £1 million in cash and film it. Hardcore social statements aside, the island offers stunning scenery over the Sound of Islay, as well as an enormous collection of Red Deer which outnumber the human population 30 to one.
6. No Man's Land, England
No Man's Fort was built in the 1800s to protect Portsmouth against attacks from the French. When that particular threat abated, the fort was sold off and reopened in April 2015 as a hotel. Only accessible by helicopter, the luxury hotel boasts its own lighthouse and a host of watersports for adrenalin-seeking guests. You'll also find a BBQ deck for marshmellow-toasting sessions under the stars, rooftop hot tubs and a Lazer Battle arena...
7. Oronsay, Scotland
This tiny island tucked away in the Inner Hebrides is only accessible from neighbouring Colonsay and Skye at low tide. Inhabited only by a few local families, Oronsay is Scottish seclusion at its very best with great views out onto the water and a ruined 14th-century Augustinian priory to explore. It's an easy walk out from Skye, but check tide times carefully before you leave to avoid stranding yourselves.
8. Burgh Island, England
Just off the south coast of Devon, Burgh Island can be reached on foot at low tide but the local hotel has come up with an unusual solution for ferrying its guests back and forth when the route is covered by water. The sea tractor will plough you out across the divide to wander the island's gorgeous beaches. The Burgh Hotel, a tribute to 1930s art-deco splendour, constantly receives top reviews for its food, spa treatments and guest rooms.
9. Saint Michael's Mount, England
Another small tidal island, this time just off the coast of Cornwall, St Michael's Mount embraces everything that it is to be quaint, old England on one rocky outcrop. Slip across on foot at low tide to discover its cobbled streets, 15th-century harbour and a castle that has been home to the St Aubyn family for generations.