Trinity Mirror’s three Sunday tabloids sell at 50p in North and Tayside areas of Scotland

However, the Sunday Mail, The Sunday Mirror and The People all reverted to their normal cover prices across the rest of the UK.

The Guardian quoted one media buying industry executive as saying: "I'm a little surprised that Trinity Mirror has done this so quickly. Is it because they can't afford it or because they don't think they can compete?

"I expected the price battle to last at least a couple of weeks. If the Mirror capitulates early then it could prompt Murdoch to move up from 50p much sooner than he had planned."

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On The Sun’s Sunday edition, one media buying source told The Guardian: "The first week there were a lot of curiosity buyers and huge free publicity because it was such an event.

"Sales show there was no major uplift for the Saturday Sun, or the first few days this [last] week. The expectation is that Sunday Sun sales will drop significantly. Cutting prices comes straight out of profit and doesn't make sense."

The Scottish Sun and the Sunday Mail, co-incidentally, yesterday both had front-page splashes on different angles to stories on disgraced Scottish Labour MP Eric Joyce.

The Scottish Sun led on a teenage girl’s first-person story on a three -month fling with the MP, while the Sunday Mail led on a tape recording by a woman constituent who sought help from Joyce on an employment problem.

Claimed the Sunday Mail: “Shamed MP Eric Joyce is today damned as a drunken, lecherous thug – in his own words.”

Inside, the Sunday Mail pointed out that the recent National Readership Survey gave it a readership of 1,024,000 which made it “easily the best-read paper in Scotland”.

It added: “They also show our sister title, the Daily Record is read by 843,000 Scots while The [Scottish] Sun is read by 822,000.”

Meanwhile, The Sunday Post mounted a major marketing exercise –devoting two-thirds of its front page to a remarkably strident promotional box.

Inside, it trumpeted: “It’s been a fantastic year for The Sunday Post with readership numbers soaring to almost 850,000. The number of people reading the Post is now 846,000 – a jump of 5.5% since this time last year.

“And our share of the Scottish Sunday newspaper market has also increased – leaping 3% to 21% in the past year.

“It means your favourite family read is leaving competitors trailing. Over the same period, the Sunday Mail’s readership fell by 0.6%, the Mail on Sunday’s was down 1.1%, the Sunday Herald’s dropped 13.5% and Scotland on Sunday slumped by 16%.”

According to News International, the Sunday launch issue of The Sun sold 3.46 million copies across the UK and 323,000 copies in Scotland.

The Sunday Mail’s latest ABC figure in January was 357,724.