Diane Dernie, whose 23-year-old son Lance Bombadier Ben Parkinson, a paratrooper, sustained multiple injuries in an Afghan mine blast, accused the Ministry of Defence of 'cynically neglecting' seriously brain-damaged soldiers.

 Although Parkinson's case forced ministers to announce changes to the much-criticised compensation rules this month, she claimed Whitehall officials had ignored pleas to address the rising number of serious brain injuries suffered by other British troops.

Dernie said: 'There are other soldiers who have suffered brain injuries from roadside bombs or mortars who get scandalously little compensation and are not covered by the changes.'

This was partly because the review had dealt just with 'multiple injuries', she said. Those who suffered only brain injuries were not covered by the review.

But it was also because the government was refusing to fix what she termed 'fundamentally unfair rules' for compensating brain-damaged soldiers. Compensation awards under the MoD's system are made on a sliding 15-level scale ranging from £1,000 to £285,000.

Soldiers who are left either in a vegetative state or 'with no meaningful response to the environment' receive the level-one maximum award. But the next level of mental injury is assessed as level-three, resulting in compensation of £115,000 rather than £201,250 at level two - even though the category can include soldiers left with 'limited response to the environment and substantial physical, sensory, personality, behavioural or cognitive problems and [requiring] skilled nursing care'.

'The difference in compensation makes a huge difference to how soldiers and their families can cope with a lifetime disability,' Dernie said. 'It is appalling that in order to save money, the government is cynically neglecting young people who have sacrificed all for their country. The worst thing is that in a way they need more care and more support than a person in a vegetative state, because they will eventually leave hospital and try to achieve some sort of life either at home or in care.'

Parkinson is being treated at Headley Court, the military rehabilitation centre in Surrey.

He lost both legs and suffered multiple injuries including to his brain and spine. His case and the government's response means he now stands to receive nearly twice the £152,000 originally offered by the Ministry of Defence. Even so, friends are fundraising to buy his mother a suitable house where she can care for him. The maximum military payout is barely half the £500,000 top award for civilian victims of violence such as the 7/7 terror attacks.

Another victim, Lance Corporal Martin Edwards, 25, suffered brain damage when a roadside bomb in Iraq shattered his helmet visor late last year. His wife, Sarah, 23, revealed that the family had been offered only the level-three compensation of about £115,000 - despite Edwards's need for lifetime care and the additional resources required to raise a 20-month-old son, Phoenix.

A ministry spokesman told The Observer the changes would not cover casualties like Edwards because he had not suffered multiple injuries. The MoD said the 'tariff levels' for brain injuries were based on existing civilian injury schemes. In the light of recent changes in guidelines for those programmes, ministry officials were examining 'future' tariffs. An overall review of the compensation scheme would not come until 2010 - after it had been running for five years.

There are no reliable figures about British soldiers who have suffered brain injuries in Iraq and Afghanistan. The MoD provides fortnightly updates on the number of 'serious' and 'very serious' injuries, but without further details.

A military welfare campaigner last night said there were other brain-injured British soldiers likely to be left behind by the compensation changes. The source said he knew of at least two other cases: both men had suffered head injuries in Iraq last year, one from a mortar blast and the other a gunshot wound.