Boris Johnson will not declare a free luxury holiday he received at the Spanish villa belonging to the Goldsmith family in the register of MPs’ interests, Downing Street has said, meaning he does not have to detail the value of the gift.

Johnson listed the near week-long stay in the Marbella property in October in the register of ministerial interests. It confirmed the holiday was provided free of charge by the family of Zac Goldsmith, the former Conservative MP who is now a peer and an environment minister.

However, this register does not detail monetary values. The separate register of MPs’ interests does but on Friday Johnson’s spokesman said the prime minister had no plans to list it there.

“Earlier this year the prime minister received hospitality from a long-standing family friend who provided their holiday home,” the spokesman said. “In line with transparency requirements, he has declared the arrangement in his ministerial capacity, given the hospitality was provided by another minister.”

Asked if this was an attempt to avoid revealing the cost, they added: “The declarations in terms of the transparency requirements have been met by the prime minister. Ministerial code declarations fall outside the remit of the Commons register.”

The unusual decision to not make a full declaration will heap pressure on Johnson. He has previously had to apologise to the parliamentary commissioner for standards, Kathryn Stone, for making incomplete or late declarations.

Stone, who is also expected to adjudicate on whether Johnson broke rules in the way he financed a refurbishment of his Downing Street flat, faced calls from ministers this week to resign after the government briefly and disastrously tried to reverse her decision over the suspension of the Tory MP Owen Paterson for breaking paid lobbying rules.

No 10 said the decision to avoid the MPs’ register was based on a section of the MPs’ code of conduct detailing the rules for registering overseas visits. Part of this states they do not need to be declared if they are “wholly unconnected with membership of the house or with the member’s parliamentary or political activities (eg family holidays),” which appears to be the No 10 argument.

While Goldsmith is a friend of Johnson’s, and particularly of the prime minister’s wife, Carrie, he was also made a peer by Johnson after he lost his Commons seat in 2019, and given a government job.

The Goldsmith family property is marketed online for rentals for as much as GBP25,000 a week. After the holiday, the Guardian revealed that documents indicated the villa had been held by an opaque offshore structure based in multiple tax havens.

The papers suggested the minister and his family may have owned the property through a Maltese company held by companies in the Turks and Caicos Islands and administered by a wealth-planning firm based in Switzerland.