Natwest's lawyers are confident of recovering £290,000 from Michael Bright's wife Katie, although Bright's lawyer has vowed to fight the action.
Reid Minty partner Stephen Moss is handling the claim for NatWest, while Davenport Lyons partner Trevor Sears is acting for the Brights.
Moss said Michael Bright had several loans with different parts of NatWest, including a mortgage with National Westminster Home Loans.
"We're suing on a joint loan account in both Mr and Mrs Bright's names," he said.
Moss refused to speculate on what defence Sears might use against the claim. He said: "We're expecting an answer from Davenport Lyons shortly. I'm awaiting their defence to see what they say."
Moss would not comment on Katie Bright's financial resources, but pointed out she had a half-interest in the couple's three properties.
However, Sears was adamant the bank had no case.
"I don't really know how they can claim any money from her," he said.
"A wife can't be responsible for her husband's debts."
Bright has put his Kent oast-house and Wapping apartment up for sale and is currently staying at his Marbella holiday house.
"Mrs Bright owns half of the property and, if she wanted to, could offer to buy Michael's half from the trustees," Sears said.
"At the moment, however, they've not decided."
Bright also owes £4.3m to HSBC for a loan taken out late last year and an undisclosed sum, believed to be a couple of hundred thousand, to the Inland Revenue.
The House of Lords in Etridge, the name of a group of appeals held together, ruled the solicitor's duty was limited to making sure the wife understood the nature and effect of the transaction.
The solicitor's role had previously been widely defined by the Court of Appeal, with solicitors having to satisfy themselves that the wife had entered into the transaction under her own free will.
This left solicitors exposed to charges of professional negligence if the business subsequently failed.
In an attempt to retain the family home, the wife would claim she had not been properly advised and had acted under the "undue influence" of her husband.
Tony Nurse-Marsh, a partner at Henmans which acted for one of the solicitors in the appeal, said the Lords had brought common sense to bear on this area of the law.