Capital Ideas, which has offices in London and Birmingham, said this morning it has offered to buy the paper from Guardian Media Group for a nominal sum, with a view to turning the brand into a weekly news magazine and website.
The idea of turning the paper into a weekly news magazine has already been mooted by Guardian Media Group. Closing it or slimming it down are the other options on the table.
The options did not include selling the paper, though a sale was rumoured to have been considered several years ago.
The publishing division of Capital Ideas said it had sent a preliminary letter to GMG containing details of the proposal.
Renwick Haddow, a consultant at Capital Ideas, said: "We are making the first overtures at the moment but we are quite serious about it. We will be talking to them."
The group, which owns the Compliance Monthly and Investing for Growth trade titles, said it would publish a weekend news magazine under The Observer brand, in the style of The Week.
If its bid were successful, Capital Ideas said it would slim down the paper's current staff considerably.
GMG said it had not yet received the letter, but hinted that any forthcoming offer would be unwelcome.
"It is not surprising, in the light of recent media coverage, that opportunistic and unsolicited approaches of this nature might be made."
Guardian Media Group will next month publish the results of a strategic company review, which may include closing The Observer or turning it into a weekly news publication.
The Observer's average six-month circulation is down 7.47% year on year to 415,566 copies.
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