Grassroots unrest in Craig Thomson’s central coast seat of Dobell is starting to stir as the ALP’s 100 local members react to the brothel brouhaha threatening to bring down the Gillard government.

Labor insiders on the usually-sleepy retirement strip have told Crikey that local branches that feed into the federal electoral council — Ourimbah-Narara Valley, Tumbi Umbi, The Entrance day branch, Wyong, Lake Munmonahra day branch, Toukley and Wamberal-Terrigal are all believed to be wavering.

The branches overwhelmingly backed Thomson — a Melbourne-based former Health Services Union national secretary — in his 2010 preselection bid against Dave Mehan but now seem to have reversed their support. Mehan is a member and NSW state conference delegate from Ourimbah-Narara, while Thomson draws his natural backing from the 30-member The Entrance branch.

Former Ourimbah-Narara Valley branch president Norm Hanscombe told Crikey this morning that it had “become obvious that a simple conclusion to this situation can’t be found.”

“His support is evaporating, people who’ve backed him solidly have stopped doing it. All the elderly branch members used to say what a lovely young man he is but I’m not sure that we all think that now.”

The feisty Hanscombe said his Ourimbah-Narara comrade Mehan would be a strong contender when preselection opens for Dobell in 14 months time. He ran unsuccessfully for Dobell in 2004 and the state seat of The Entrance in this year’s NSW poll. The super fund manager famously challenged Thomson for pre-selection in early 2010 but lost the grassroots vote 66-21.

Those numbers are now teetering. Under NSW ALP rules preselections are decided by a 100% local vote, unless the dreaded “N40” is introduced which reduces the influence to a 50-50 split with Sussex Street. A Thomson resignation would force a byelection and a fresh preselection process in Dobell, held by Labor by 5.1%.

Multiple sources confirmed to Crikey this morning that Dobell members– many of them lifers — were once happy to go along with Thomson given his hallowed status on the green leather, but that sentiment had waned since the credit card claims got renewed airplay in a notorious radio interview three weeks ago with 2UE’s Michael Smith. Many are starting to question whether Thomson’s 2007 parachute into Dobell from south of the Murray was worth it.

And some additional pressure could be coming from party elders. One amusing angle missed by the Daily Telegraph in its coverage of the “bus debts” owed by Thomson from the 2010 campaign this morning was that the bus’ owner Daniel Parish is the son of Kevin Parish, an ALP life member and the chairman of the commuter council of NSW.

A further development has been the emergence of an energised former state MP for Wyong, David Harris, on the Dobell federal electoral council. While Harris is yet to garner a support base there, the move is seen as a pre-cursor to a serious tilt when the time comes.

Thomson’s last pillar of support would appear to come from newly-elected FEC secretary Cheryl Greenwald and a dwindling core of backers in The Entrance. Insiders report that loyal staffers Matt Burke and Criselee Stevens, both named in his maiden speech to Parliament in 2008, appear to have vacated Dobell for greener pastures, although it’s not known whether their relocation is related to the current scandal.

Whatever the outcome of George Brandis’ badgering of the NSW Police to investigate Thomson’s activities, there is little chance of the economics committee chair renominating for 2013. It leaves the prospect of a cleanskin candidate or a committed local in the mould of Harris or Mehan.

Labor scored a 1.1% swing towards it last year, but on current polling would be wiped out in a by-election. Still, for the moment the likelihood of that occurring is slim — for Thomson to be investigated for theft or fraud a complaint would need to be lodged by the federal branch of the Health Services Union. HSU national president Michael Williamson has for years served as Thomson’s mentor and is also junior vice president of federal Labor.

Thomson’s Parliament House phone repeatedly rang out this morning when Crikey tried to contact him for comment.