The Times has learnt that counsel has been instructed by the Law Society, which represents 100,000 solicitors in England and Wales, to examine the prospect of a judicial review challenge.

MPs are expected today to add their support to the society and 20 leading charities and advice groups in condemning the plans in a special debate at Westminster.

This will be the only opportunity for parliamentary scrutiny of the proposals to revamp the 50-year-old scheme, because they do not require primary legislation.

More than 800 solicitors’ offices are expected go out of business under plans to move the legal aid scheme to a market-based model, with law firms competing for legal aid contracts.

Des Hudson, chief executive of the Law Society, said: “We are very much in favour of reforming the legal aid system. But there are very real risks associated with the proposals as they stand, and we are troubled by the pace of these changes, which we believe is dangerously overhasty.”

He challenged the conconcept of competitive tendering. “If a solicitor fails to win the contract in your area to do legal aid work, then you won’t be in business for the next round of competitive tendering. So how does this process survive beyond the first round?”

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