National Westminster Bank is attacking both Bank of Scotland's and Royal Bank of Scotland's hostile take-over bid plans as too risky.
Natwest's double bid defence document slams both plans, setting the scene for a full-scale bidding war in the new year.
Both Scottish banks' plans were rejected on the grounds of their IT plans and the ability of management to deliver total cost savings.
The rejection means both banks are loosing the chance of securing a recommendation from the Natwest board.
Analysts predict the ultimate victor will be RBS, in spite of the lower value of its bid.