The Legal Services Complaints Commissioner said different awards were being made depending on a "bewildering array" of circumstances, such as support from a local MP and conduct of solicitors involved in taking claims.

A second investigation by the commissioner, Zahida Manzoor, into compensation schemes for respiratory disease and a condition known as vibration white finger, found that the Legal Complaints Service (LCS) risked damaging its reputation because of its "poor service" to some miners and their families.

"I highlight the case of six individual miners who, in 2007, have shown real persistence in their complaints. Despite being encouraged to conciliate by the LCS they refused, and insisted that their complaints should be investigated and adjudicate.

"Through their persistence, each of these miners has, on average, correctly received an additional £1,700 compensation from their solicitors."

Ms Manzoor warned that miners' complaints could become an "Achilles heel" for the LCS if it did not act on her proposals, such as good management and administrative checks and balances.