The Prince of Wales joked on his 70th birthday about the trials and tribulations of getting older as he met a room full of septuagenarians.

Charles cut a birthday cake, was handed presents and gave an impromptu speech when he had tea with group of 70 people who also turn 70 this year like the heir to the throne.

When the prince arrived for the celebration at Spencer House with the Duchess of Cornwall he was asked by the waiting press how he felt.

He replied “How am I feeling? Older, older.”

He joked: “I’m not sure, it’s rather like indigestion, many happy returns are not quite the same thing as you get older.”

Theresa May has led the nation in paying tribute to Charles and she highlighted his positive role in bringing up his sons who lost their mother Diana, Princess of Wales, at a young age.

The Prime Minister, opening a Commons debate to mark the occasion, said the heir to the throne had spent his life “defying expectations and refusing to be categorised”.

She told MPs his sons – the Duke of Cambridge and Duke of Sussex – were a “true credit to their father”, adding: “We as a nation are immensely proud of them and I am sure he is too.”

Mrs May said Charles was often seen to be “a man ahead of his time”, citing his warnings on pollution, sustainable agriculture and the dehumanising effects of technology in the workplace.

She said: “Throughout the Prince of Wales’s life, his commitment to public service has been total.”

In a recent documentary Camilla has said her husband is driven to help others and when asked if he will slow down, as his family appear to want, the heir to the throne said: “I don’t know, you may see it slowly but surely”

Camilla was asked if she had found a present for the man she has previously said is a difficult person to buy gifts for.

The duchess replied: “I did but I’m not telling you.”

Charles was given a gift by the waiting press and when he saw a 70th birthday branded balloon he joked: “I didn’t know you specialised in balloons.”

He also accepted a glittering bag containing a spray product to ward off his beloved red squirrels from bird tables, and said laughing “Where do you find these horrible things?”

Charles and Camilla travelled from Clarence House to nearby Spencer house – the former home of Diana, Princess of Wales’ family – to meet the special septuagenarians.

The birthday reception was organised by The Sun newspaper, which selected the 70 guests who are volunteers actively involved with a number of royal couple’s charities including the Prince’s Trust, the Silver Line, Maggie’s and Barnardo’s.

Age UK tea party
The Prince of Wales and the Duchess of Cornwall are presented with a book from photographer Arthur Edwards (Paul Edwards/The Sun/PA)

The Spencer family last lived in the 18th-century London mansion in the 1920s and today it is leased to the investment company RIT Capital Partners, chaired by Lord Rothschild, which has renovated the property.

As soon as the couple walked into the building the group of 70 people began singing Happy Birthday to the prince before they all posed for a photograph.

In the Great Room, the largest and most imposing of Spencer House’s state rooms, the guests gathered for the reception where they were given champagne.

With champagne flutes in her hand the group listened as The Sun’s veteran royal photographer Arthur Edwards paid a heartfelt tribute to the prince.

Charles gave an impromptu speech in return and also highlighted the achievements of the photographer.

Before cutting a birthday cake, the prince quipped: “I was asked just now outside whether I was going to slow down, I’m not sure I’ve got much alternative.”

Raymond Penrose was nominated to attend the birthday bash for playing Father Christmas in his village for 40 years, raising thousands for charity and working with disabled children.

Mr Penrose, of Chalfont-St-Giles, Buckinghamshire, said: “I feel very privileged to be here today, especially because it is Prince Charles’s actual birthday.

“It is a beautiful place to spend the day.”

Another reader nominated by The Sun, Gillian Ackers, volunteers as a home visitor for the RSPCA and undertakes weekly visits to schools to help reluctant readers.

She travelled from Quorn, Leicestershire, for the event.

Gillian, a retired magistrate, said: “I am so pleased that Charles has chosen to spend his birthday meeting other 70 year-olds.

“I am a bit surprised but very honoured to have been chosen by The Sun.

“Since I retired at 70 I try to keep busy. If I had one piece of advice for the prince on his birthday it would be that he should not stop working.”