Tourists took to the website to warn other guests away from visiting the Queen’s official residence after discovering large parts of the gardens were off-limits.

The 39-acre gardens were opened this summer for self-guided tours and picnics for the first time after entry into the palace exhibitions was halted last year.

Tickets went on sale in April at £16.50 for an adult or £42 for a family with up to three children.

The palace website promised visitors the chance to enjoy the “beauty and calm of this walled oasis” on a self-guided tour, along with the chance of a “once-in-a-lifetime opportunity to picnic on the lawn”.

But guests were left disappointed with their experience, citing overbearing security guards, a ban on prosecco, overpriced food and ‘rip-off’ gift shop items as reasons not to visit.

One guest called it a “money-making machine” while another added they felt “robbed by the royals”.

One guest wrote on TripAdvisor: “Beware of this complete rip-off! I paid £16.50 for access to the gardens only hoping to laze around, see beautiful flowers and trees.

“What I experienced was first a long queue to security check and then seeing a piece of a lawn surrounded by standing stewards watching your every step and ropes segregating rest of the garden.

“This small fragment of the park that you have access to is easily walkable around in 10 min and nothing is interesting to see there.

“You can’t even sit on the lake’s bank to watch wildlife because of these ropes everywhere. I am very disappointed and feel robbed by royals.”

Another described it as a “waste of time and money” while one person added there was “nothing special” about their visit.

Many also criticised the size of the area which was made available to the public.

One wrote: “Gardens are a waste of time and money. Large portions cordoned off. Takes less than 1 hour to get around. Also expensive coffee and cake.”

Despite the negative reviews, the palace has a 4.5 star rating — out of 5 — on TripAdvisor with almost 30,000 reviews.

One review described their visit to the gardens as “very colourful and very neat” with “friendly staff”.

A Royal Collection Trust spokesperson said: “A ticket to visit the garden at Buckingham Palace this summer costs £16.50 for adults and allows visitors to take in approximately two-thirds of the garden, including the 156-metre herbaceous border, the horse-chestnut avenue, the plane trees planted by Queen Victoria and Prince Albert, and the lawns with views of the island and its beehives across the lake.

“The opportunity to enjoy a picnic on the lawns is also part of the visit for the first time, and short talks and QR codes offer visitors more information about the garden and its history.

“Features in the south-west of the garden, including the rose garden and wildflower meadow, can be viewed through add-on guided tours, which must be booked in advance and are priced at £6.50 for adults.

“This information is detailed on the Royal Collection Trust website at the time of booking. A range of concession prices is also available.”