A British millionaire couple who are turning a Swiss castle into their dream family home allegedly owe their builders £664,000 for work on the 13th-century pile, local media reports.

Steinegg Castle in Hüttwilen, northern Switzerland, was bought in 2006 by Yvonne Thom and James Rennie, who are both reported to work in the financial sector. 

Work on the castle, which was valued at around £4million at the time, is set to cost around 12 million Swiss francs, or £10million, and has reportedly taken years to complete.

Updates reportedly include the building of an underground car park beneath the former luxury hotel and spa. 

‘We have been working up there for ten years,’ construction company director Christian Hagen told a local newspaper.

He claimed that the couple had recently failed to pay several bills, and that his firm had spoken with them to reach an agreement.

They acknowledged the amount they owed the firm, he said, but the payment has still not arrived months later.

‘We have had to wait for the money for around a year and a half now and manage without it,’ Mr Hagen said.

Works are said to include the building of an underground car park beneath the former hotel

Steinegg Castle in Hüttwilen, northern Switzerland, was bought by financier Yvonne Thom and her husband James Rennie

The firm’s contact with the long-term clients had been ‘pleasant’, Mr Hagen said, and they had met with them regularly on the construction site prior to the dispute.

He said they had made payments on time for years before the latest invoice, he said, adding that the amount is ‘a large sum’ for his family-run company to go without.

The couple, who previously lived in the castle and whose children attended a nearby private school, according to Mr Hagen, are now based abroad.

He said the situation was made more difficult due to the pair being out of the country.

They had last been in touch with the construction company in September, with an attempt to contact them in October reportedly going unanswered.

‘The path to finding a joint solution for the outstanding bill did not work out as we had hoped,’ Mr Hagen said, while adding that he has no ill will towards the clients.

Christian Hagen, who is the director of family-run construction firm H.Hagen AG

While his company is not at an immediate loss due to the unpaid sum, he said, it has meant they have been unable to invest in other areas and securing the payment has been ‘time-consuming’. 

Mr Hagen said his firm has engaged a lawyer and has decided to file for enforcement proceedings to secure the sum.

‘Of course we want the money that we are entitled to, that would be the case for everyone,’ he said. ‘We just have to be patient.’ 

Ms Thom and Mr Rennie could not be reached for comment.