Shares in stricken British mortgage bank Northern Rock tumbled over 6 percent on Monday amid concerns that potential bidders will steer clear as the turmoil in global financial markets deepens.

With three potential bidders having had a look, but the advisors asking for more creative solutions, we raise the possibility that the equity is not worth anything at all, said Bruce Packard, analyst at Pali International.

By 7:12 a.m. EST the bank's shares were down 6.4 percent at 160.4 pence, after hitting 160p, down 13 percent in the last three days and cutting the bank's market value to under 700 million pounds ($1.5 billion).

Other European bank shares also fell sharply for a third straight day, hit by fears about more big industry losses after U.S. giant Citigroup warned of more write-offs.

Northern Rock investors were unsettled this could deter bidders or hamper their financing plans.

Richard Branson's Virgin Group-led consortium and U.S. buyout firm JC Flowers have confirmed their interest in the bank. Cerberus, another Wall Street firm, is also interested, sources familiar with the situation have said.

All three will want the government to keep a funding guarantee in place, a source said last week, and Pali's Packard said none of the trio were likely to bid without it.

He said in a research note the value of the equity was highly dependent on normal funding conditions returning and maintained a sell rating on the shares.

Advisers for Northern Rock have sent out a broad information memorandum to potential bidders, seen as an attempt to revive interest from trade buyers or elsewhere in a break-up or other solution of the bank, which has been engulfed in crisis since needing emergency funding from the Bank of England six weeks ago.

A weekend report said as much as 14 billion pounds had been withdrawn by Northern Rock depositors since the crisis broke, far higher than other estimates. A spokesman said that was a significant overestimate, but declined to comment further.

Northern Rock has borrowed about 23 billion pounds from the BoE in emergency loans since September 14, according to the BoE's weekly balance sheet data, regarded as the best estimated of the scale of loans.