Mill told The Scotsman that if the new independent complaints handling body - the Scottish Legal Complaints Commission - is empowered to impose such a penalty on solicitors it would be "nothing less than naked lawyer-bashing."
He says: "When IPS was introduced 15 years or so ago, the level stood at 1,000 and it was quite wrong that that level was not increased for a long time, but when they did increase it, it went from 1,000 to 5,000 literally overnight.
"Having read the English Clementi White Paper, the figure the English body is being given is 20,000. That would be an entirely inappropriate figure for the Scottish marketplace, for a range of reasons. A 20-fold increase in penalty in two or three years is nothing less than naked lawyer-bashing.
"It will be a test of the true courage and independence of the Executive to see what they come up with because there is a suspicion they are simply being led by the nose by the English here. The Law Society in England and Wales has admitted a failure to handle complaints. We do not have the record of failure that they do. We just hope the Executive doesn't take the easy way out, which is really just replicating the provisions that were necessary in England and which would be entirely unnecessary, and possibly even unaffordable, in Scotland."
The Executive has set up a working group to consider the Scottish implications of the English White Paper - The Future of Legal Services - Putting Consumers First - which is closely based on the proposals made by Sir David Clementi in 2004. But the Scottish working group will not report until after the publication of the Legal Profession and Legal Assistance Bill, due this Thursday, which will flesh out the detailed proposals for the new independent complaints commission, announced in December.
Mill adds that if the SLSC is granted the power to impose a penalty of 20,000 on solicitors, it could have serious implications for the viability of high street firms and access to justice in rural areas.
"Our concern is not so much the big firms - they don't get complaints because they don't do the kind of work that produces complaints. But high-street firms doing repossessions, summary crime, matrimonial work and so on get a complaints experience. If they are potentially fined up to 20,000 in a case, that will cause these firms either, where possible, to pass that cost on to the client base and, where that won't be appropriate - and it won't be for legal aid or most of the client base firms like these carry - it will peril the future of these firms."
John MacKinnon, vice president elect of the society and a partner with Brown & McRae in Fraserburgh, says the changes to complaint-handling could have serious implications for recruitment.
"We have grave concerns about what will happen in a small practice like mine and in a small town like Fraserburgh," he says. "There is a huge problem with professionals already - we can't attract doctors, we can't attract dentists, we have difficulty attracting solicitors. In Fraserburgh, there are about 12 solicitors but only one under 40." MacKinnon adds that if a 20,000 penalty were to be imposed it could make it harder to resolve complaints at the early stages. "If they were to go down the same road as in England and increase the compensation to 20,000, I think we would be less able to sort it out at source."
Michael Clancy, the society's director of law reform, also warns the revamp of complaint-handling could undermine access to justice. He says: "Certain practices don't have the capacity to pass on their costs," he says. "I am thinking about practices in rural areas and small towns and practices that are the backbone of access to justice in this country, through the legal aid system.
"Ultimately, if we want a system that provides an overall service throughout the country, which gives access to justice and allows us to comply with ECHR [European Court of Human Rights] in giving independent advice on civil rights and obligations and criminal law, we have got to think strategically. A change to the complaints system could have a potentially damaging consequence."
The new bill is also expected to clarify how solicitors will fund the new complaints-handling commission. Mill says it would almost certainly cost significantly more than the current complaint-handling system, on which the society spends 2.1 million a year. "I don't see this body costing less than 4 million or 5 million a year," he says. "There is also a hidden subsidy of at least a million pounds because 2.1 million is what we actually spend. But each of the client relations committees is staffed 50/50 between solicitors and lay representatives. Sure, we pay these people expenses, but they are giving a huge subsidy of time to the process."
He adds: "There are 13,000 solicitors whose names are on the roll just now. Of them 10,000 are in practice. Of them, about 2,700 of them are what we call in-house lawyers, including fiscals. So, will they pay the levy to this body?
"If it is going to cost 4 million or 5 million, what percentage of that is going to be raised by the profession and what percentage is the state going to properly pay? The Executive are going to save about 400,000 by decommissioning the [Scottish Legal Services] Ombudsman's office, so we really feel at least that contribution should be made from the state."
He adds there is also concern about how solicitors should be charged: "Is it a per capita levy? Or is it 30 per cent levy and 70 per cent 'polluter pays' or the other way around? 'Polluter pays' is one of these sexy expressions that sounds quite good. But it is not bad lawyers creating complaints, it is the client base creating the complaint."
A spokeswoman for the Executive confirmed the bill is due to be published on Thursday. However, she adds it would not be appropriate to pre-empt the findings of the Scottish Clementi working group.