The Law Society has failed to properly investigate miners' complaints against their solicitors, a legal watchdog said today.

Legal Services Ombudsman Zahida Manzoor said the solicitors' professional body had "failed to act in an impartial manner".

The long-running compensation process involves hundreds of thousands of claims for industrial diseases linked with working in the pits.

There are 580,000 claimants for respiratory problems and 170,000 for vibration white finger, estimated to cost the government £7 billion to settle by 2011.

M s Manzoor's special inquiry examined the Law Society's handling of hundreds of complaints about "inadequate professional service".

The ombudsman's report said: "I was concerned to learn that some complainants or their families may have felt pressurised into accepting solutions that were not the best outcome for them.

"I was equally concerned to hear that some miners had given their authorisation for their MPs to act on their behalf, but nevertheless the Law Society have routinely bypassed the MPs involved and contacted the complainants directly."

She said she had investigated eight individual cases with seven more pending.

"I anticipate that I could receive many hundreds of complaints during the course of the next year or so if the Law Society's approach to resolving these cases remains unaltered."

Among a list of shortcomings, the ombudsman said the Law Society had "failed to adopt a neutral stance when seeking to conciliate the complaint".

It had also failed to obtain relevant papers and failed to take account of the circumstances of each case.

"In all, the Law Society failed to properly investigate the miners' complaints," she said.

"I take the view that in these cases the Law Society adopted an unthinking acceptance of blanket conciliation proposals which had been advanced by the very solicitors complained of. I think that was entirely wrong."

The ombudsman has used her powers to make the Law Society re-investigate the cases.

Earlier this year, the Law Society advised solicitors to repay to miners any money that had been wrongly deducted from compensation payments.

Ms Manzoor has also called for compensation to be paid for any inadequate professional service and for any distress and inconvenience caused.

Yesterday Ms Manzoor, in her capacity as Legal Services Complaints Commissioner, warned that the Law Society was facing a fine after she rejected its plan for handling complaints from customers.

Ms Manzoor said the Law Society - which represents 121,000 solicitors in England and Wales - had failed to include her targets in its plan for the next financial year.

The Law Society said the number of solicitors facing allegations of misconduct over miners' compensation who have been referred to the Solicitors Disciplinary Tribunal has now climbed to 45.

The series of probes relating to the handling miners' compensation claims was "by far the biggest in the history of the Law Society", said a spokesman.

Chairman of the Law Society Regulation Board Peter Williamson said: "These figures are powerful evidence of our determination to deal firmly with any misconduct related to the miners' compensation scheme."

The Law Society is taking out advertisements to tell former miners who received compensation how to get help in checking their claim was dealt with properly.