Image copyright Bright Dairy Image caption The Queen's grandson Peter Phillips is shown endorsing Jersey milk in a series of adverts in China

It evokes a quintessentially English image of lush green fields and grand stately homes and ends with the Queen's grandson taking a satisfying sip of fresh milk.

A Chinese television advertisement, unearthed by the Daily Mail this week, shows Princess Anne's son, Peter Phillips, endorsing milk from Jersey cows and comes as the Duke and Duchess of Sussex prepare for a new life of greater financial independence.

Despite not having a royal title and never having been a working royal, Mr Phillips, 42, is introduced to viewers as a "British Royal Family member" while he is pictured in various regal settings in the campaign, which aired on Shanghai television.

At one point he says of the milk, via a Chinese voiceover translated by BBC Monitoring: "It's fresh, and it's what I want".

The Mail revealed on Wednesday that another of Prince Harry's cousins, Lady Kitty Spencer, 29, has also worked with a separate Chinese milk brand on a campaign partly filmed at the British Museum.

It raises the question of whether Prince Harry and Meghan might pursue similar work as they take more control over their finances.

For royal biographer Penny Junor, the sight of a person with royal connections using their status for financial gain "always looks bad".

"It does not reflect well on the monarchy," she told the BBC - though she adds there is an attraction to such deals. "It is difficult," she said. "I understand the need to feed a family."

Image copyright PA Media Image caption Peter Phillips and his wife Autumn Kelly sold pictures of their 2008 wedding at Windsor to Hello! magazine

Royal observers said that, in reality, there is little to stop those born into the ancestral Royal Family - but who have not taken official working royal roles - from pursuing commercial opportunities.

"Peter Phillips was absolutely entitled to do what he likes because he is not a member of the Royal Family," royal commentator Ingrid Seward told the BBC's PM programme.

"He is by blood but he doesn't ever represent the Queen, he doesn't represent the Crown, he has never taken public funds and he doesn't do any royal duties and therefore he can do what he likes."

While this may be the case, Buckingham Palace suggests on its website that the use of Royal Family members - including Peter Phillips - for commercial purposes should be approved beforehand.

Image copyright Getty Images Image caption Lady Kitty Spencer has also appeared in a Chinese milk campaign - although she is not a member of the Royal Family by blood, she is Prince Harry's cousin

Former Home Office minister Norman Baker said strict rules governing royal endorsements have been broken and has written to the Cabinet Secretary Sir Mark Sedwill to express his concern.

In the letter, seen by the BBC, Mr Baker wrote: "The word 'royal' is of course strictly controlled by the royal names team in the Cabinet Office.

"Can I ask whether permission was sought and given for the use of the word 'royal' to sell milk? Assuming it was not, what steps do you and your colleagues intend to take to end this use immediately?"

A Cabinet Office source said the matter was not one for the department.

'Uphold Queen's values''

In a statement from Buckingham Palace last week, Prince Harry and Meghan are described as making clear "everything they do will continue to uphold the values of Her Majesty".

And a palace source told the Times: "The values we usually talk about are the Nolan principles of public life. But obviously the view was taken within the family that those sorts of things will be discussed".

The Royal Household said in its latest annual report that it endorses the so-called Nolan principles of public life when it comes to the declaration of interests and that it is "active in maintaining high standards of conduct in relation to its employees and officials".

The seven principles were first set out by the late Lord Nolan in 1995 and are included in the Ministerial code for elected officials.

What are the Nolan principles of public life?

Selflessness Integrity Objectivity Accountability Openness Honesty Leadership

Source: Gov.uk

Those who are royal by blood rather than by title - as the Sussexes will soon be - are unlikely to have to seek permission from Buckingham Palace before endorsing products or appearing in advertisements, according to Ingrid Seward.

"I think they have to be sensible and maybe ask advice," she added. "It is a very difficult tightrope to walk and basically you have to run everything you want to do by a committee of people."

Yet Penny Junor said that approach might not work for Prince Harry and Meghan - who are set to gain as much freedom as Peter Phillips by setting aside their official royal status later this year.

Meghan has already secured work with entertainment giant Disney in return for a donation to an elephant conservation charity, while Harry's sports' links could be attractive to potential sponsors.

Image copyright EPA Image caption Meghan's acting skills could see her secure further work for entertainment companies like Disney

"With Harry and Meghan, everyone knows who they are. They do not need their royal titles to make money," Ms Junor said.

"The spirit of the agreement seems to be that they won't use their royal status for financial gain.

"But I'm not sure their American advisors are in tune with the subtleties of the British Royal Family."

The couple have also placed an application to trademark their Sussex Royal moniker, covering merchandise including books, clothing and calendars.

In his letter to the cabinet secretary, Norman Baker asked what guidance was sought prior to the Sussexes' application.

Buckingham Palace said it does not speak on behalf of Mr Phillips and did not respond to the BBC's broader questions about protocols and procedures regarding commercial deals.