A Tasmanian senator is under fire for the refurbishment of an office in the state's north-west, which cost taxpayers over half a million dollars, but he says he will not apologise as "Canberra money" went into the pockets of local small business and local pay packets.

Key points: Steve Martin fell out with Jacqui Lambie in February, with her accusing him of disloyalty and expelling him from her party

Steve Martin fell out with Jacqui Lambie in February, with her accusing him of disloyalty and expelling him from her party Senator Martin deemed Ms Lambie's former electoral office in Burnie too far away from Devonport

Senator Martin deemed Ms Lambie's former electoral office in Burnie too far away from Devonport Senator Martin said the cost of the office refurbishment in Devonport was higher "because of rules about the security"

Nationals senator Steve Martin opted to set up his parliamentary office in Devonport's Rooke Street, declining to take over former senator Jacqui Lambie's office in Burnie, a distance of about 46 kilometres to the west.

Ms Lambie's former electoral office in Mount Street, which was refurbished in 2014, remains vacant.

Senator Martin, a former mayor of Devonport before he was confirmed by the High Court as Ms Lambie's duly elected replacement, told the ABC he requested to have his office located in Devonport to ensure "efficiency" and "practicality".

"Being the only Nationals senator for Tasmania, I have to cover the whole of the state," he said.

"I am better off to access the whole of the state from Devonport rather than a 40-minute drive there and a 40-minute drive back just to go to the office."

In a statement, Senator Martin said he would not apologise for bringing a significant amount of money from Canberra to Tasmania's north-west region.

"This is an investment of over $500,000 of federal money coming into the state, employing local tradesmen and local businesses," he said.

Steve Martin faces an uphill battle to retain his senate seat at the next election, an expert says. ( ABC News: Nick Haggarty )

The senator said the Department of Finance controlled the refurbishment and he did not have a say in the size and fit-out of the office, but requested contractors from regional Tasmania be used.

"Costs are likely to be higher than for a regular business because of rules about the security of the elected federal member and his or her staff," according to Senator Martin's spokesperson, who added the issue "has been handled in the same way as it would be for any of Tasmania's other 16 federal MPs and senators".

Steve Martin and Jacqui Lambie in happier times. ( ABC News )

In answers from the Department of Finance to questions asked by Labor at a budget estimates hearing in November, it was confirmed an estimated $531,000 was spent on the refurbishment, excluding GST.

Labor Braddon MP Justine Keay is now the only federal politician to have their office based in Burnie, with Senator Martin joining Liberal senator Richard Colbeck and Labor senator Anne Urquhart in Devonport.

Ms Keay, who is also Devonport-based, said she drove to work in Burnie on a daily basis and described the use of taxpayers' money on Senator Martin's office as "unacceptable".

"A 40-minute drive is no excuse for spending that amount. I was offered to move offices but chose not to because of costs," she said.

Ms Lambie, who expelled Senator Martin from the Jacqui Lambie Network after he denied her request to stand aside and clear the way for her return, said she expected Tasmanian voters to take the spending into account at the next federal election.

"I think it is a shame that taxpayers have had to spend money on outfitting a new office when there was absolutely nothing wrong with the one in Burnie," she said.

Senator Steve Martin (centre) with National Party leader Michael McCormack and deputy leader Bridget McKenzie in Launceston. ( ABC News: Declan Gooch )

Tasmanian election analyst Kevin Bonham said given his short term, it would be a challenge for Senator Martin to keep his seat at the federal election next year.

"It's fairly difficult because he's only been there for a short time and he hasn't had a lot of chances to build a profile as a senator," he said.

Mr Bonham also said the changes to Senate preferencing require candidates to get either a strong primary vote or sufficient preferences from voters to be elected, which Mr Martin may struggle to do.

"I think it's going to be very hard for him to get more than a few per cent, given he's had so little time to make an impact," he said.