The British royal family has defended spending a seven-figure sum refurbishing the Duke and Duchess of Cambridge’s Kensington Palace apartment.

The taxpayer will foot the bill for extensive work on the property, including installing a new roof, overhauling the electrics and carrying out significant plumbing works.

A royal spokesman said repairs and refurbishments – reported to cost in the region of £4 million ($A7.30 million), though this figure was not confirmed by the royal household – would also see a “significant amount of internal building” to “return the residence to function as a living space”.

William and Kate’s Kensington Palace apartment was designed by Sir Christopher Wren and was the home of Princess Margaret and Lord Snowdon. Margaret remained there after their divorce and lived there until her death in 2002.

The living space was last refurbished in 1963.

“This is the Duke and Duchess’s one and only official residence. It is here that they plan to stay for many, many years to come,” a royal spokesman said.

“We also had to take into account the fact that Kensington Palace is a scheduled ancient monument, and all elements of the refurbishment had to be agreed with English Heritage. Often this meant ensuring a high standard of work in line with the historical significance of the Christopher Wren building.”

He said William and Kate “paid privately” for all the internal furnishings, including carpets and curtains. They were also at pains to ensure that the specification is not extravagant.

“As with any other part of the estate, it was the royal household (TRH) who were responsible for the refurbishment of the residence – where they could in the course of the procurement process, TRH helped to bear down on cost,” he added.

“The household oversaw the planning, tendering and project management of the refurbishment and were responsible for the budget and spend.”