Negotiations: China's president Xi Jinping is believed to have made some tweaks to the details of his banquet at Buckingham Palace

State visits are always a minefield of diplomatic niceties, and none more so than the imminent arrival of the Chinese president.

But while most would assume that the issue of human rights and China’s annexation of Tibet would be the most pressing issues on the table, in fact it’s the fish.

According to royal sources, the visiting Chinese delegation, led by President Xi Jinping, and his wife, Peng Liyuan, have politely declined the proposed seasonal Turbot and crab starter at the welcome Buckingham Palace luncheon because they will only consume cured or smoked fish.

And Prince William, who will also attend the lunch with his wife, the Duchess of Cambridge, won’t eat the accompanying coriander sauce.

To cap it all, apparently the Chinese wish to bring their own water, perhaps not entirely trusting of the home-grown stuff.

By all accounts, talks between the Royal Household and their Chinese opposite numbers have been exceedingly cordial.

In fact the Chinese have made clear that they are looking forward to the ‘Royal Chef’, Mark Flanagan, and his team preparing their meals.

The talented team in the palace’s cavernous kitchens use occasions such as state banquets and luncheons to showcase meat, game, fruit and vegetables from the Queen’s estates as well as promoting the ‘best of British’.

The attention to detail is remarkable, with the even the post dinner chocolates being moulded from the button on a footman’s livery and dusted with edible gold.

There will be two showpiece events on the first day of their visit on October 20, a luncheon at Buckingham Palace which follows a full-scale ceremonial welcome, followed by a glittering state banquet later that night.

Seasonal: But turbot has been rejected as a starter course by the visiting Chinese delegation

The banquet will be attended for the first time by the Duke and Duchess of Cambridge, with Kate wearing one of the Queen’s tiaras.

Intriguingly, it will also be new Labour leader Jeremy Corbyn’s inaugural royal event and fashion watchers are likely to be keeping as close an eye on what he is wearing as the fashionable Duchess.

Prince Charles, the Mail understands, does not intend to attend the evening’s festivities because of his strong personal opposition to the country’s treatment of Tibet – although final negotiations over the issue were due to take place last night.

The prince counts the country’s spiritual leader, the Dalai Lama, as a personal friend and once memorably described China’s communist leaders as ‘appalling old waxworks’.

He has boycotted previous state visits in 1999 and 2005, although in recent years has developed several charitable initiatives in China and met the previous president when he attended the G20 summit in London in 2009.

However he and his wife will be attending the official welcome at Horse Guards Parade and are expected to attend the lunch thrown by the Queen afterwards at Buckingham Palace, along with Prince Philip (who once memorably told students during a 1986 tour of China that they would become ‘slitty-eyed’) as well as the Cambridges.

Welcome: The Queen is hosting a formal state banquet for China's head of state to kick-start his visit to the UK

Buckingham Palace declined to comment on which members of the Royal Family were taking part in the visit or what would be served but insisted there had been ‘no issues’ over the menus.

‘The Household and Chinese officials have enjoyed excellent cooperation in preparing for the State Visit. We don’t recognise any of the issues you describe,’ they said.

But a source close to the planning of the event told the Mail that a proposed menu for seasonal butternut squash with turbot, crab and a coriander sauce had not been vetoed.

Although the Queen is particularly partial to turbot, a species of North Sea flatfish highly prized for its delicate flavour, she had been told that the Chinese wouldn’t touch it because of their caution in eating fish from local waters - something the Queen herself steers away from when abroad – and would prefer cured or smoked fish.

Prince William’s staff also made clear that he wouldn’t eat coriander, while the Duchess of Cornwall apparently isn’t fond of venison or goose.

Kate, however, was said to be ‘happy to eat anything’ and had no particular view on what white or red was served, but was not keen on spirits.

‘As for drinks, it has been noted that the president will be bringing his own water to drink,’ the source said.