Here on the Illawarra coast, south of Sydney, spring sparkled on Saturday. Some bushwalked, some went hang-gliding; others filled the beaches, cafes and pubs.

This hedonism extended to another - perhaps guilty - pleasure: giving the Labor Party a ferocious caning in the Cunningham by-election.

At close of counting yesterday it was almost certain that the Greens had broken into the Australian House of Representatives. Simon Crean will now cop the heat, but he can plead extenuating circumstances.

Cunningham is an unusual seat. At federal elections, usually even the bluest-ribbon Labor electorates contain affluent Liberal enclaves. Not here, where the wealthy booths vote Labor too.

The old mining towns from Austinmer to Stanwell Park have received hordes of sea-changing inner-Sydneysiders over the past decade.

Many commute to the state capital and others remain economically well-plugged; average incomes are high, house prices are Sydneyesque and the lattes flow freely.

Wollongong, a half-hour drive down the coast, is a large town with collapsing industry and smoke, drugs, crime and unemployment. Much of the work is low-skill.

Cunningham covers both of these, and at last year's federal election swung to the Coalition by 7 per cent.

Despite this, it remained safe for Labor's Stephen Martin - vis à vis the Liberal Party at least.

The Libs didn't run last Saturday and would have had no chance had they done so. What happened on Saturday was an internal squabble, a fight between the community-based Left and the mainstream Centre-Left. Perversely, it seems to have been decided by the Right (Liberal voters.)

The Labor Party is not popular. Anger at ALP local council-developer hanky-panky erupted last month with the election of an independent lord mayor. The manner of Martin's departure from politics and the foisting by Labor's head office of its own candidate still get a good run in the local Illawarra Mercury.

Disaffected unionists found expression in independent Peter Wilson, bourgeois lefties in the Green Michael Organ. These two swapped preferences. (So close were their camps that at my polling booth they shared a table.) De facto Liberal David Moulds, who beat Wilson into third place, preferenced the Greens ahead of Labor.

Everyone did - 12 in all. Simon Crean can't entirely escape blame. A leader with authority might have stemmed the tide.

But Cunningham is symptomatic of wider changes. The nationwide anti-conservative vote continues to splinter. Opinion polls show that while Labor's stocks are low, the broad left vote is reasonably healthy.

This is not as bad for Labor as might appear. Under compulsory preferential voting, you must number every square, and the vast majority of Green voters would sooner gnaw off their arm than put Tory before Labor.

It was preferential voting that did Labor in at Cunningham, turning a 38 to 24 per cent first-preference lead into a loss. But preferential voting keeps Labor competitive with the Coalition.

Peter Brent lives in Cunningham and is editor of mumble.com.au, a website that looks at electoral behaviour.