Many dream of taking on a renovation project, something to transform and make your own.

But for one former software company owner, the opportunity to bring back to life a derelict 19th Century Napoleonic fort brought with it more challenges than he had ever anticipated.

Mike Conner, 52, snapped up Thorne Island near Milford Haven in Pembrokeshire for £555,000 in May 2017.

The building, which was known for its parties under a previous owner, had been empty for 17 years, taking him about a year to bring it to a habitable state.

Now equipped with 40 beds, four en-suite bathrooms and its own night club, the historic building has come a long way from having no running water, and is back on the market for £3m.

“Many have described it as a midlife crisis,” Mr Conner joked.

“I really didn’t know what I was getting myself into.”

Layered with history, the 100-man fort was originally built in the 1850s to protect the busy port of Milford Haven from French naval attacks.

A proposal was first made in 1817 to fortify the island but it was not implemented until sometime after 1852.

A date of 1854 has been carved above the island’s entrance, according to the island’s website.

It was converted into a hotel in 1947 and hired out for birthday parties, weddings and stag parties, before being sold in 1999.

By 2001 the building was bought by the Von Essen hotel group who intended to spend £4m to re-open the hotel, equipped with a cable car to allow access from the mainland.

But it was largely abandoned when Mr Conner purchased the listed building, with the once-bustling party island left to grow over.

“There was no electric, no water, and any food or waste needed to come back off,” he said.

“My wife was pretty cross when I first said I bought it, she said she would stay once it had a flushing loo, which is pretty reasonable.”

But Mr Conner did not anticipate the first flush would require cutting through 16ft (5m) of rock to get to the biodigester pump, ultimately costing him £200,000.

“Wales has got some absolutely fabulous historic buildings that are in really sad states,” said Mr Conner.

The whole Thorne Island renovation process took nearly five years to get over the line, with six men living on the island for about four years while work was ongoing.

Much of the equipment was brought in via helicopter, Mr Conner said, a process he described as “incredibly hard” given its location.

He added getting materials was extremely difficult, but it was also a challenge for those who agreed to work on the project and live on site.

“Most people who joined the project, I still work with now,” said Mr Conner.

“You just couldn’t predict how many people want to help you.”

The men working on the island would spend stints of about two weeks on the island, unable to shower and covered in dust.

“They would charge their phones with a generator, and would have to have a dip in the sea for a wash. It was tough living,” said Mr Conner.

Mr Conner, who trained as a design and technology teacher, said the design process excited him the most.

He said he could not believe the Victorians could build something so magnificent, inspiring him to keep going.

He added: “A thousand men were working on it for two years, it was built in the same way as Stonehenge.”

“I felt my task was really modernising it,” Mr Conner said, adding the renovation was a task of figuring out how the new would work with the old.

“It almost feels like a tribute to their hard work and you’re just really building the last little bit on top of what was already an awesome, bomb-proof construction.”

The island has “seen everything”, according to Mr Conner, from 80-people parties to “millpond serenity”.

With “no neighbours to upset”, the island hosted its own festival for Mr Conner’s 50th birthday, complete with a tight-rope performer across the picturesque courtyard.

“People who come for a weekend are surprised when I hand them a bin liner and say it needs to come back off with them – but no-one comes here to collect the bins.”

As a former CEO, Mr Conner described his time on the island as “incredible” as he had to let go of everyday routines.

“We all often live by a calendar of scheduled meetings, but the island is the complete opposite – it’s off grid. It feels real time, it feels like living.”

Time stops on the island, Mr Conner said, adding that with something always going on, people tended to put their phones away.

“I think that’s what makes Thorne a special place, that people are present.”

Originally from Gloucestershire, Mr Conner does not live on the island but as the primary contractor spent a lot of time there during the renovation process.

He initially juggled running his business alongside the venture, but sold his software company two years ago.

“It was quite cathartic for me to have this parallel life of complete chaos, which particularly through Covid was quite awesome.”

The project also lifted the lid on Mr Conner’s personal heritage too, as it was not until he got the keys did he discover he is in fact a quarter Welsh, as his mum grew up at Upton Castle, Pembroke Dock.

Speaking of the island’s future, Mr Conner said he hoped its new owner enjoys it as much as he has, but that it also has huge potential to operate as a tourist attraction, or play host to “the most unbelievable raves”.

Mr Conner said he envisaged the site offering an “unbelievable 24-hour experience”, with the potential to host about 800 people.

“I think that would be great for Wales, but I’m not in that industry and I don’t know how that works.

“If it was generating revenue, and creating jobs and sustaining itself, that would be a great outcome.

“The more people who could use it the better, as it’s got to be one of the most interesting buildings in the area,” he added.

Mr Conner said more people needed to come to Wales and see what is there.

“It’s a blank canvas, and the next owner can work out what it’s for,” he said, speaking of the island.

“But if there are any events there, I would crawl over broken glass to get there.”