Perth’s newspaper war has jacked up a notch with News Limited’s Sunday Times set to launch a Saturday “lunchbox edition” next week to take on bitter rival The West Australian, Crikey can reveal.

The Times‘ newsroom, which was whirring on all cylinders this morning to produce a trial edition to iron out any last minute kinks, is believed to be up in arms over the changes, which will force some hacks to file their scoops up to 24-hours earlier.

The deadline for the new Saturday edition will be around midday on Saturday, but most stories will need to be filed by Friday night, with the paper to appear on Perth streets at approximately 1:30pm, a source close to the paper said. In an echo of Hey Hey It’s Saturday‘s shift to Wednesday, the Saturday Sunday Times will retain its “Sunday” masthead.

The current Sunday version will continue to be produced, but will contain little in the way of fresh content.

The strategic move is expected to escalate tensions between the Kerry Stokes-controlled West Australian — Perth’s sole weekday newspaper — which last week said it would launch its new Weekend West title tomorrow, promising an “all-weekend read of news, opinion, information and entertainment”. The Weekend West will remain a Saturday, but like The Weekend Australian would feature both a Saturday and Sunday dateline.

A major motivation for the News Limited salvo is to allow The Times a foothold in Perth’s booming weekend real estate advertising market, which is currently dominated by The West. It will also allow The Sunday Times to be shipped earlier to the state’s booming north.

This week, West Australian editor Brett McCarthy denied he was treading on The Sunday Times‘ territory, saying that “We both live well, apart from each other”. McCarthy was the former editor of The Sunday Times until 2007 before later defecting to WAN in 2009.

Rumours have been circulating about a Saturday Sunday Times for months, with McCarthy believed to be aware of the move well in advance. An industry insider told Crikey that the savvy editor had launched The Weekend West as a preemptive strike on his former employer.

In the three months to June, The Sunday Times‘ circulation stood at 303,581, with the Saturday West Australian on 333,768. However, another Times source said the new edition would only add around 3-4,000 to that figure, considering consumers would be unlikely to buy the same paper twice, adding that the “suicidal” strategy was “completely mad” and a “complete f-cking disaster”.

Secretary of the WA Branch of the Media Entertainment and Arts Alliance, Michael Sinclair-Jones, told Crikey that the union “would be watching very closely how the move pans out.”

“We would be concerned if people were expected to work extra hours for nothing,” he said. Sinclair-Jones said he would be meeting with Sunday Times staff on another matter today and would raise the issue of the extra edition.

Crikey understands that The Australian has known about The Sunday Times‘ shift to a Saturday edition for months but has decided not to publish anything to protect News Limited’s corporate interests in its war with WAN.

Sunday Times editor Sam Weir, who did not return calls, is in Sydney this week meeting News Limited global boss Rupert Murdoch. Sources close to the paper say that Weir is believed to be preparing to plaster an animal on the paper’s front page to satiate the mogul’s demands for “bespoke editions” during his local jaunt, as documented by former Herald Sun editor-in-chief Bruce Guthrie in his book ‘Man Bites Murdoch’.