Katherine Grainger and Anna Watkins win World gold in Slovenia

Katherine Grainger and Anna Watkins produced a dominant display to win Britain's first Olympic class gold medal at the World Championships.

The defending double sculls champions led from start to finish with Australia in second and New Zealand third.

British men's pair Andy Hodge and Pete Reed were beaten into silver by reigning champions Hamish Bond and Eric Murray of New Zealand.

In the single sculls, Britain's Alan Campbell had to settle for bronze.

Grainger, a three-time Olympic silver medallist, and Watkins arrived in Slovenia as overwhelming favourites for gold having not been beaten since they became a pair in January 2010.

Earlier in the season, Watkins missed a World Cup regatta with a back injury, but the pair reunited in Lucerne in July to win one of four British golds.

Their performance was equally impressive in Bled, leading from the start and stretching their lead to 2.35 seconds at three-quarters distance before easing off in the final 500m.

"It was a fantastic race for us - really, really challenging," said Grainger, who won her sixth world title in nine years.

Watkins added: "It was a much tougher run into the World Championships this year.

"It was a huge challenge and we rose to it brilliantly, and it's absolutely the best preparation for [the London Olympics] next year."

There was more pain for Hodge and Reed who suffered their 14th consecutive defeat at the hands of Kiwis Bond and Murray.

The New Zealanders exploded out of the blocks, pulling out a lead of a length over Britain after 500m.

They increased their lead over the next 1000m and although the British pair fought back, upping their stroke rate to 42 per minute, the Kiwis had enough left in the tank to ease across the line to win by 1.5 secs.

It means Hodge and Reed are likely to move into the coxless four boat for London 2012.

"That was a fast race, almost world record pace," said Hodge. "Whatever happens next, it will be the same for every single member of the GB team aiming for London.

"We will go away and train harder, be more determined and totally focused on the next 11 months."

Campbell had to settle for bronze for the second consecutive year with a typically dogged performance in the final race of the day.

The 28-year-old, who has struggled for fitness this season, made his trademark fast start, leading the field at half distance.

But four-time world champion Mahe Drysdale of New Zealand and defending champion Ondrej Synek of the Czech Republic hauled themselves back into contention as Campbell began to fade.

Drysdale held his nerve to reclaim the title he last won in 2009 ahead of Synek, with Campbell 4.81 seconds further back.

"I would have liked to get the gold in this race but it was so painful in the second half," said Campbell.

"I had to take the risk [to go out quickly]. I wanted to stretch the field out."

With more finals to come tomorrow, Britain has already qualified 13 of a potential 14 boats rowers for London 2012.