The Law Society has accused the government of hiding key information on which it based controversial new personal injury fees.

The Ministry of Justice has rejected the society’s freedom of information request for the full report into the future reform of the RTA Portal extension.

Ministers plan to push ahead with slashed recoverable costs for low-value claims and expanding the system for employer and public liability claims, although it is still uncertain when these will come into force.

Two claimant groups, the Association of Personal Injury Lawyers and Motor Accident Solicitors Society, will go to the High Court next week to put forward the case for a judicial review into how the reforms were made.

In a similar vein, the Law Society is demanding to know why it cannot be shown the full Fenn report, a study completed last year to look into the future of the portal. The Society has now requested a review of the decision not to disclose the full details of the report.

Chief executive Desmond Hudson said: ‘Presumably the government commissioned the factual study to inform its thinking on how fixed costs might be changed.

‘The government should base its policy-making on a sound factual basis. The alternative is that the government’s proposals are based on ministers’ own preconceived ideas or on lobbying from the insurance sector.

‘We believe that the government is hiding behind a misapplication of the Freedom of Information Act in order to save its blushes.’

A consultation on reducing fixed costs from £1,200 to £500 for RTA claims up to £10,000 ended on 4 January. A spokesman for the MoJ said there was still no update on its response.

There was also no further comment on the extension of the portal, which justice secretary Chris Grayling postponed in December, promising further comment ‘in the new year’.

Both the new fees and the extension had been expected on 1 April, when a host of other civil justice reforms are due to be implemented.