It was supposed to be a hero's homecoming, but Warilla gold medallist David Smith's journey from the London Olympics back to the Illawarra took an unexpected turn yesterday.

Hours after touching down in Australia after his emphatic victory in the K4 1000m men's kayaking event in London, Smith was slugged $700 by a vigilant police officer for driving an unregistered vehicle.

Smith and his girlfriend, Australian sailing silver medallist Nina Curtis, were on the final leg of their return trip to Wollongong when the officer pulled them over in Engadine.

It was a bitter pill to swallow for the 25-year-old, who had parked the car in Sydney while he trained his way to Olympic glory.

"I've been overseas for the past four months and unfortunately the car ran out of registration a week ago," Smith said.

"We landed and jumped into the car to drive home, and then the next you know, the sirens came on.

"We haven't got emails or received paperwork, and the last thing you look at after being four months away is your car registration when you go for a drive.

"I'm a bit disappointed with the fact I got a $700 fine, but oh well, it's the law - what can you do?"

Asked whether he had considered dangling his gold medal in front of the officer in a bid to explain his simple oversight, Smith said: "I don't think that was going to help. We gave him the story that we'd just got home from the Olympics and he wasn't really interested."

The incident capped a turbulent 24 hours for Smith.

Earlier, he and the rest of the Australian Olympic team were given a rousing reception at their official welcome home in Sydney.

About 500 guests, including the Prime Minister, greeted the Olympians in a Qantas hangar at Sydney Airport.

Smith is the Illawarra's first Olympic gold medallist since 1972, and his win was one of Australia's seven gold-winning performances at the Games.

"It's pretty exciting that people are acknowledging my achievements in that way, I really appreciate it," he said. "It's slowly sinking in, having people come up and ask for autographs and photos, and people I don't know recognising me and saying 'hey, you're one of those K4 guys'."

Smith will take a break before training for the Rio 2016 Games.