Royal Bank of Scotland today set the stage for a dramatic head-to-head battle with Barclays for control of Dutch bank ABN Amro as it told investors it would be ready to take its €71 billion (£48 billion) bid directly to shareholders in mid-July.

RBS and its partners Fortis Bank and Banco Santander told the stock market they expected to file all draft offer documents to Dutch regulator AFM and the UK Listing Authority "by early next week". Special shareholder meetings will be called by all three banks during the following days.

A public filing to the US Securities and Exchange Commission is expected to follow by the middle of next month. "The offer to ABN Amro shareholders is expected to commence at this point," the three banks said.

Just ten days ago Barclays told investors that it had virtually completed preparations for its €65 billion offer and would be launching its formal bid "in July". Barclays said it had submitted filings to 107 regulators in 52 countries.

The prospect of a bid showdown over ABN Amro comes as Barclays comes under pressure from Atticus, an activist investor, to drop its bid on price grounds.

The bank has been trying to find ways of sweetening the terms of its bid without asking its investors to stump up more cash or have their shareholdings further diluted. Atticus reiterated its opposition in a conference call with Barclays chief executive John Varley on Wednesday.

Both sides have made it clear that they don't want to overpay. Within the RBS consortium , Fortis has said it will not improve terms.

The bid is complicated by the proposed sale of ABN's American arm LaSalle, currently frozen by a Dutch court. The RBS trio is thought to prefer waiting until the Dutch Supreme Court rules on whether a $21 billion sale of LaSalle to Bank of America can go ahead before launching its offer.

Bank of America has threatened to sue anyone that thwarts the deal but has held previous settlement talks with RBS, which has taken reserves to cover legal action.

It is understood that no recent talks with Bank of America have taken place and that the consortium is determined to press ahead irrespective of the legal threat.

RBS lost 8.5p to 632.5p, while Barclays fell 6.5p to 722p.

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