MARLBOROUGH'S royal guest, Prince Charles, will be popping into Waitrose supermarket during his walkabout in the town next week.

Details of the itinerary of his visit next Friday as part of Marlborough's 800th anniversary celebrations are such a closely guarded secret that staff in the store did not know about it until yesterday.

One shop worker said: "The news is only just filtering through."

Store manager Neil Westbrook said they would be thrilled to see the royal visitor, although it will only be a brief glimpse.

The prince will be using the shop as a means of reaching the High Street after visiting Hilliers Yard behind the store and viewing its recent extension, as well as the site of the proposed Riverbank theatre/cinema.

Waitrose, which is one of the biggest single employers in Marlborough, stocks a full range of Prince Charles' own Duchy of Cornwall products, everything from sausages and ham to cartons of gravy.

The store opened more than 20 years ago in the High Street with its site incorporating the town's old cinema.

Four years ago it underwent a huge extension and revamp and is regarded as the flagship of the Waitrose retail chain.

It is the architecture and not the store itself that interests Prince Charles, according to a Clarence House spokeswoman.

He is interested in new uses for old buildings, she said, and will see how the upmarket store is hidden behind a faade that has changed little in centuries.

The store's High Street entrance was where people from the town used to queue to buy tickets to see movies in Marlborough's only picture house, The Cinema, that closed in 1970.

It is understood Prince Charles will be interested not only in the way the original Grade II listed faade was retained but also in the design of the building, especially the extension whose external features mirror those on centuries old buildings nearby.

The prince is due to arrive in town at around 10.45am at Marlborough College.

After unveiling a commemorative stone on the site of King John's hunting lodge, he is due to leave the college at about 11.30am and walk along the High Street, arriving at Waitrose at 11.50am.

Waitrose's development director Nigel Burton will escort Prince Charles down Hillier's Yard to the back of the store giving an opportunity for the royal visitor to see how the shop was designed to fit in with its location.

Prince Charles will meet the store's architects and will then walk through the shop and out past the checkout desks and through the front entrance.

Once back in the High Street, at about 12.05pm, the prince will go on a traditional royal walkabout meeting local people, schools and groups, before crossing, at 12.15pm, to the Merchant's House, the home of wealthy 17th century silk merchant Thomas Bayly that is undergoing restoration.

Prince Charles will be shown over the Merchant's House by the chairman of its trustees, Sir John Sykes.

He will then continue his walkabout the crowds will be kept behind barriers to the newly-revamped town hall where the Mayor, Coun Graham Francis, will officially welcome him to Marlborough.

He will unveil another commemorative plaque outside the town hall before going inside to a half-hour reception where he will meet invited representatives of local groups, organisations and services.