Guardian News and Media/London

Buckingham Palace, a leading cinema chain and one of Britain’s best known art galleries are among a group of high profile employers who sign staff up to so-called “zero-hours” contracts to keep employment costs at a minimum.

Two days after it emerged that retailer Sports Direct employs 20,000 staff on zero-hours terms, the Guardian has established that the royal family’s London residence, along with Cineworld and the Tate galleries, hire workers under the controversial employment practice.

The 350 part-time employees deployed as extra staff during Buckingham Palace’s summer opening have no guaranteed hours. They work in the shop, greet visitors, and work as monitors in the rooms made open to the public.

All of Cineworld’s part-time multiplex staff are on zero-hours contracts, as are all catering staff at the Tate galleries in London, Liverpool and St Ives, Cornwall.

Buckingham Palace opened its doors to the public earlier this week, but all the temporary staff hired to run the State Rooms attraction, which includes a Diamond Jubilee exhibition, are forced to sign contracts which give them no guarantee of any work.

However, although the contract leaves staff with no promise of work, they are not allowed to work for any other employee without written permission from the palace.

A copy of a staff contract seen by the Guardian, dated 2009, says: “Your hours of work will be advised by the visitor manager and will be dependent upon the requirements for retail assistants at Buckingham Palace as and when required.

“You are employed to work exclusively for Royal Collection Enterprises Ltd (a palace subsidiary) and if you wish to seek secondary employment you must first obtain the written consent of your head of department.”

A spokeswoman for the palace said the contracts did not guarantee any amount of work, but said rotas were drawn up a month in advance for staff to plan their hours. But she declined to characterise them as zero-hours contracts. “All temporary staff employed during the summer opening of Buckingham Palace are issued with fixed-term employment contracts for a three-or four-month period. These are not zero-hours contracts.”

The palace argues that because the staff are entitled to certain benefits on days when they are called in, such as a free hot or cold lunch, holiday pay and uniforms, amongst other benefits, they cannot be described as zero-hours.

The Office for National Statistics estimates that 200,000 staff work on zero-hours contracts. But experts now believe the true number is far higher.

Cineworld, the UK’s second biggest cinema chain with 80 sites across the country, uses zero-hours contracts exclusively for its entire part-time workforce at its multiplexes. With 4,500 employees working at the cinemas and in head office, it is thought that up to 80% are on zero-hours contracts.

Cineworld declined to comment.