The Duke of Edinburgh has admitted ahead of his 90th birthday how he is reducing his workload before he reaches his "sell-by date".

Last night, however, the Royal was back in action, as a blaze of colour, a burst of cannon fire and a rousing display of pageantry greeted him on the eve of his birthday at the beating retreat on Horseguards Parade.

Philip took the salute at the annual event in central London, watched by some 4,000 members of the public seated in stands around the vast parade ground.

As the clock struck 9pm he walked into the ground dressed in his Grenadier Guards uniform.

Philip, who is Colonel of the Grenadier Guards, saluted as the massed band opened with a rendition of the National Anthem, their music ringing out through the chill night air.

In a wide-ranging television interview broadcast earlier to mark the milestone, Philip discussed his life, work and interests over the past nine decades.

But the Royal, who has been the Queen's constant public companion for more than 60 years and involved with around 800 charities and organisations, stressed how he was "winding down" and looking forward to enjoying himself in his dotage.

The Royal celebrates his 90th birthday today and even said his memory was going and, in his outspoken style, how he favoured discrimination against older people as "you go downhill" in your later years.

The Duke was unapologetic about his most infamous quip - describing the Chinese as "slitty eyed" - during the interview with Fiona Bruce for the BBC documentary, The Duke At 90.

And the long-term conservationist, who was international president of the World Wildlife Fund, railed against those who are overly concerned about animal welfare, describing them as "bunny huggers".

Philip was reluctant to give his views when questioned about his early years, which saw him brought up by his grandmother in England after his parents split up, or comment on how he had made a "success" of himself.

Interviewed in Buckingham Palace, the Royal said: "I reckon I've done my bit, I want to enjoy myself for a bit now. With less responsibility, less rushing about, less preparation, less trying to think of something to say. On top of that your memory's going, I can't remember names. Yes, I'm just sort of winding down."

Last autumn it was announced how the Duke was lightening his obligations by relinquishing his attachment to a number of his more demanding organisations including his patronage of UK Athletics, City and Guilds of London Institute, the Royal Agricultural Society of the Commonwealth and his involvement with a number of high-profile universities.

The Earl of Wessex, interviewed for the documentary, believed his father remained just as busy: "He keeps on saying he's trying to slow down but I haven't seen much evidence of that, he seems to fill the gaps with lots of other things, which is fantastic."

But Philip stressed how it was time for him to take a back seat: "You don't want nonagenarians as heads of organisations which are trying to do something useful. There is an ageism in this country, and quite rightly so, because I think you go downhill - physically, mentally and everything."

Bruce countered by saying some of his charities would not describe him as being past his sell-by date but the Duke replied: "No, it's better to get out before you reach the sell-by date".