Howard, campaigning in Liberal MP Jamie Briggs’ Adelaide Hills seat of Mayo today, has launched a broadside at Xenophon, calling on the South Australian senator to declare which party he would support in a hung parliament.

Howard says Xenophon needs to declare his allegiances if he wants to move away from single-issue politics.

“His anti-poker machine stance caught the popular mood. But he’s gone far beyond that now,” Howard told FIVEaa radio.

“He’s representing himself as having an attitude about everything.

“When you’re in that position, you’ve really got to declare yourself and you can’t have it both ways.

“You can’t have the purity of abstinent independence but have a view on everything.”

Howard attacked Xenophon’s protectionist stance on free trade agreements, saying he should remember what carried Australia through the global financial crisis.

“How anyone would pussy-foot around embracing those free trade agreements is beyond me,” he said.

Xenophon, however, fired back, criticising Howard’s government for entering into “badly negotiated free trade agreements that compromised local jobs and increased our trade deficit”.

“Free trade agreements are a good thing if they are negotiated with our national economic interest in mind. The fact that the trade deficit with China has increased at 15 per cent a year since the Howard-era FTA says it all.”

Xenophon said Howard’s criticism was a sign of how panicked some sitting Liberals were.

“At a personal level, I’ve always liked John Howard, and I’m very grateful that he’s given the Nick Xenophon Team so much oxygen in SA with his attack,” Xenophon said.

“Deep down I think he must really like me, as evidenced by his comments on me following the 2013 election.”

From the sidelines, Labor leader Bill Shorten described the stoush as bizarre, considering the pair shared similar views on reducing penalty rates.

“I heard the Liberal Party called John Howard off the bench to come and help beleaguered Jamie Briggs in Mayo,” Shorten said in Adelaide.

“This is the reunion of the Work Choices warriors.”

Polling shows Xenophon’s candidate Rebekha Sharkie is a chance to unseat Briggs in Mayo, a seat that has always been in Liberal hands but has shown itself to be vulnerable to a strong third-party or independent candidate.

The Liberals have given the seat more attention than usual, with Prime Minister Malcolm Turnbull visiting Mayo last week to promise funding for sports facilities in Mt Barker.

Singer John Schumann, representing the Australian Democrats in Mayo, came close to unseating Howard era Minister Downer in 1998, polling more than 22 per cent of the primary vote. The Democrats had also polled well in Mayo at the 1990 election, and lawyer Brian Deegan, standing as an independent, attracted 15 per cent of the primary vote in 2004.

– with AAP