Energy Secretary Ed Davey spoke movingly about his disabled son yesterday, insisting he will not let anyone ‘write him off’.

The Lib Dem minister takes his son John, who cannot walk or talk, to Hungary for treatment at the Peto Institute which specialises in teaching children how to move.

Mr Davey said when he tried to get NHS treatment when John was a baby, he was offered occupational therapy, speech therapy and physiotherapy, all of which had 12 months waiting lists.

‘We said thanks, but no thanks,’ Mr Davey said.

John was initially diagnosed with cerebral palsy but tests at Great Ormond Street Hospital have found that diagnosis was wrong. It is not clear what he is suffering from.

‘John is my joy, he’s five in November, but he has a few difficulties,’ Mr Davey told a Liberal Democrat fringe event. ‘He can’t walk or talk but he can understand you. He’s got a mean sense of humour.’

Mr Davey described his frustration at how disabled children were often treated as though they were stupid.

‘I would never let anyone write off my son,’ he said. ‘People write off cerebral palsy children because they can’t speak.’

Mr Davey and his wife Emily have to massage their son for 45 minutes a day because he can’t move his limbs.

Despite this, Mr Davey said, ‘he’s quite a strong little thing’.

The 46-year-old, who has been tipped as a future party leader, was also asked about his own hard childhood.

Mr Davey lost his father at four. His mother then suffered breast cancer which developed into terminal bone cancer when he was 15.

He had to look after her when she was in severe pain. ‘It was not a good time,’ he said.

‘It was very difficult for me and it’s obviously influenced what I think about life and to take one practical example that’s the need to support young carers.’

After losing her, he questioned why he had to keep striving academically at school.

‘I worked hard at school to please my mother and she was no longer there,’ he said.

Mr Davey said he only really got angry at life when his grandfather died.

‘Bereavement makes you more self-reliant and resilient and determined,’ he said.