The solicitors' body was accused of negligence, breach of statutory duty and mishandling complaints by Peggy Wood, 77, who said she had lost her home because of professional misconduct by her solicitors.
Ole Hansen, a friend allowed by the court to speak on Miss Wood's behalf, said: 'At the heart of my case is that, during the entire period of dealings with the Law Society, the society's dual role of both protecting and regulating the legal profession gave rise to conflicts of interest which officers and members consistently resolved in the interests of the profession as opposed to members of the public - myself in particular.'
Miss Wood is asking Mr Justice Otton to award her damages in an action which could stand as a test case.
Mr Hansen said: 'If the Law Society had intervened, simply properly using its normal investigative and disciplinary machinery, then it is more likely than not she would not have been thrown out of her home.'
The case centres on advice Miss Wood received from solicitors Hubbard and Co, of Chichester, West Sussex, 20 years ago. She alleges they wrongly acted for both sides when they arranged loans for her to develop her land.
She also claims they failed to tell her that one loan was supplied by a company, Mobile Homes (Borden) Ltd, which was part owned by Joseph Hubbard - husband of the partner who acted for Miss Wood.
She was eventually evicted from her home and moved to a Salvation Army hostel. She was left with pounds 1,400 after her debts were paid.
A letter Miss Wood wrote to the Law Society in 1979 is said to have shown clear prima facie evidence of a conflict of interests in the actions of Hubbards.
But the society's professional purposes department declined to investigate, taking the view that the firm had acted in accordance with its duty to its client, Mobile Homes.
The hearing continues today.