Prince Philip told a Filipino nurse on Wednesday that her country "must be half empty – you're all here running the NHS" – in a demonstration that his ability to raise eyebrows remains undiminished at the age of 91.

The Duke of Edinburgh made the comment during a visit to Luton and Dunstable hospital to open a £5.5m cardiac centre. The nurse appeared to take the comment in good humour and laughed before the duke moved on.

The visit was his first engagement of the year after his Christmas break at Sandringham in Norfolk. A spokeswoman for the hospital described the royal visit as a huge boost for staff morale. The duke described himself as being in a "jovial" mood, adding that he was the "world's most experienced curtain puller". He also asked when the hospital would be building a helipad to save him the journey by car.

The duke is well renowned for making gaffes. He famously told British students during a 1986 state visit to China: "If you stay here much longer, you'll all be slitty-eyed." He also once told a group of deaf youngsters: "Deaf? If you are near there, no wonder you are deaf," referring to a school's steel band. In 1995 he asked a Scottish driving instructor: "How do you keep the natives off the booze long enough to pass the test?"

He also caused controversy in 1999 in Edinburgh when he saw an untidy fuse box during a tour of a factory. "It looks as though it was put in by an Indian," he said. The prince once told Olusegun Obasanjo, president of Nigeria, who was in national dress, "You look like you're ready for bed" and described Ethiopian art as "the kind of thing my daughter would bring back from school art lessons".

Buckingham Palace rarely comments on the prince's jokes and Wednesday was no different.

A spokesman said: "We do not comment on private conversations."

The hospital spokesman said of Wednesday's visit: "Staff greatly enjoyed the opportunity to meet the Duke of Edinburgh, and we regard all personal conversations he had with our staff and guests as private and therefore would not comment on them.

"Luton is a very cosmopolitan town and the working staff at Luton and Dunstable hospital reflects that."

The duke had a stent fitted to clear a blockage in a coronary artery in December 2011 and when, during the visit, he was given a gold plated stent, he quipped that he now had a spare.