Mr Law, who is jointly and severally liable with them as a guarantor, has had his name added to their writ demanding the removal of their guarantor status on the grounds that they were misled by previous chairman John Partridge as to the state of the company during negotiations for its purchase.
An approach by the guarantors to settle the matter out of court was strongly rebuffed by John Partridge's lawyers in November.
The Law/Mellor/Jemmett writ to strike out the guarantees followed legal action by Mr Partridge and his fellow creditors after it became clear that the final payment - £1.33m - in the £14m purchase deal agreed in 2005 would not be paid by November 16 last year.
The rival claims have been accompanied by bitter personal attacks on both sides and seem almost certain to end in court.
John Partridge and his son Frank have attacked the bid to have the guarantees struck out as a cynical attempt on the part of Mellor, Jemmett and Law to avoid paying the £1.3m owed, dismissing the guarantors' claims as "absolute fantasy".
Mr Law has indicated that he intends to take further legal action over sums he told ATG he had refunded customers with regard to problems relating to objects purchased during the John Partridge era.
Much of the basis of the guarantors' complaint is that John and Frank Partridge, in particular, were party to fraudulent transactions involving fakes during their stewardship of the company, accusations they strongly deny.
Mr Law told ATG that it was only in the spring of 2006, a few months after he and his fellow directors bought the company, that they first became concerned about what had gone on before.
When asked why it took them until the end of 2009 - following the placing into administration in July and later sale of the company - to go public and pursue a legal course, Mr Law said it was because considerable fresh evidence had come to light from a new source in September 2009.
In their writ the guarantors cite eight cases where they argue that customers were defrauded "by dishonest descriptions and provenances" linked to counterfeit furniture. They further argue that refunds linked to these cases were not clearly shown in the company's accounts, leading to a false picture of financial performance and the value of Partridge Fine Arts Ltd, a public company.
The guarantors say that both these factors would have serious implications for the company's reputation and future prosperity, and the purchasers, led by Mr Law, should have been made aware of them during negotiations to acquire the company.
For their part, the Partridges deny any wrongdoing, dismiss the claims as "absolute fantasy" and accuse Law, Mellor and Jemmett of creating "trumped-up allegations".
It is thought that it could take up to a year before the claims are heard in court.
By Ivan Macquisten