Sydney - Australian Prime Minister Tony Abbott marked his country's national day on Monday by honouring Britain's Prince Philip with a knighthood, sparking criticism from the opposition of being in a "time warp".Abbott said Queen Elizabeth II had accepted his recommendation that her husband, the Duke of Edinburgh, be awarded the nation's highest honour as a Knight of the Order of Australia."This honour recognises the contribution of the Duke of Edinburgh to Australia throughout the Queen's sixty-two year reign," the conservative leader and keen monarchist said in a statement."Prince Philip's long life of service and dedication should be honoured by Australia," he said, adding that Prince Philip's son Charles, the Prince of Wales, was appointed a Knight of the Order of Australia in 1981.Mature debateAbbott reintroduced knights and dames to the country's honours list in 2014, prompting ridicule from opposition Labour lawmakers who said it was proof the prime minister was behind the times.Republicans, who are in favour of cutting Australia's ties to the British monarchy, accused Abbott at the time of "turning the clock back to a colonial frame of mind that we have outgrown as a nation".Opposition leader Bill Shorten, who on the weekend called for a mature debate on becoming a republic and having an Australian head of state, said the surprise decision was out of step with the public mindset."I think that on Australia Day - where we're talking about Australia, Australian identity - the government's managed to find a British royal to give a medal to, a knighthood to," he told Fairfax radio."I just think giving our top award to a British royal is anachronistic. To be honest it's a bit of a time warp. I wasn't quite sure it was serious until I realised it was."Inspiration and wellspringShorten said his complaint was not with Prince Philip, simply the fact he is a British royal."Why would we give him our top Australian honour? He's already got a lot of them," he said.Abbott defended his decision, saying the queen's husband is the patron of hundreds of Australian organisations and the "inspiration and wellspring" of the Duke of Edinburgh awards which have provided leadership training to tens of thousands of young people.Asked to respond to criticism on social media, much of which has appeared under the hashtag #jokeknighthood, he replied: "I'll leave social media to its own devices."Social media is kind of like electronic graffiti and I think that in the media you make a big mistake to pay too much attention to social media," he told reporters."The monarchy has been an important part of Australia's life since 1788 and Prince Philip has been a great servant of Australia," he said.Great honour"I am just really pleased in his 90s, towards the end of a life of service and duty, we in this country are able to properly acknowledge what he has done for us."Prince Philip, who is known for his politically incorrect gaffes, asked an Aboriginal businessman on a 2002 trip to Australia: "Do you still throw spears at each other?"Prince Philip was named a knight along with retired Air Chief Marshal Angus Houston, who led Australia's initial response to the missing Malaysia Airlines aircraft MH370 and downed flight MH17 in Ukraine.Houston, who served in the armed forces for more than 40 years and became Chief of the Defence Force in 2005 before retiring in 2011, said he was surprised by the honour."I am still Angus Houston and most of the things I've been involved in have involved leadership, but I would be very quick to say that it's the people I've worked with that have delivered the outcomes that have been achieved," he told the ABC."It's a great honour to be recognised in this way but I'd like people to still call me Angus."Knights and dames were introduced into Australia's system of honours in 1976 by then-prime minister Malcolm Fraser, but abolished a decade later by Bob Hawke. Previously, Australians had been honoured through the British Imperial System.