But Bob Diamond, Barclays chief executive John Varley's righthand man in the bid for the Dutch bank, has also hinted that RBS and its partners, Fortis and Santander, might be taking on dangerous risk in the current volatile climate for banking shares.
He said the consortium's 71 billion (48bn) offer "will probably beat ours" if the rival group sticks with its offer amid the current financial market turmoil involving subprime worries and risky debt vehicles.
Diamond said at a conference in New York: "The bad news is if the consortium still wants to pay that price, if it's comfortable with the risks on the balance sheet during the turmoil, if they can raise that money in the market and if regulators are going to allow this kind of complex transaction, then that price will probably beat ours."
However, he added: "But there are a lot of 'ifs' between now and then. We have to take into context that the market environment has changed. Do we still want ABN? Yes."
A sharp fall in share prices in recent weeks means that Barclays offer, which is 37 per cent in cash, is currently about 12bn less than the bid from the consortium, which is 93 per cent in cash.
Fortis still needs to raise 13bn through a share issue to pay for its part of the bid for ABN.
It comes amid speculation that the RBS consortium, whose offer for ABN was made at the height of the M&A boom, may try to lower its 38 a share bid, which is trading at a significant premium to the ABN share price.
Sources have said it is possible for the consortium to invoke a so-called material adverse change clause to lower their price, although they said there had so far been no discussions to do so.
The sources said the RBS group may make a decision closer to the date its offer is due to expire, on 5 October. Barclays's offer is due to close on 4 October.
Banks such as Barclays, RBS and the big US bulge bracket investment banks, have come under increasing pressure in recent weeks to disclose their exposure to US subprime mortgages and leveraged loans linked to private equity deals. Meanwhile, Diamond said that Barclays Capital, the arm of Barclays behind several investment vehicles hit hard by the credit crunch, still managed to post a profit during August.
He said: "Barclays Capital traded profitably in August 2007, after full allocation of costs and the mark to market of all positions. This was on the back of a profitably July. Year to date profits are well ahead of 2006."
• The RBS consortium yesterday launched a website in English and Dutch aimed at addressing any concerns that ABN staff may have about their future following any successful takeover of the group by the consortium. RBS boss Sir Fred Goodwin says on it that ABN "has a lot of very good people".