MEGA-SONS of mega- mothers are bringing family names into disrepute. The Queen's 'heir deferred' is blaming his family, especially his father, for his infidelity to his unwanted wife. And the former Prime Minister's son is keeping mum about whether he profited from her power. Both these boys are nothing without their families, however.

Mark Thatcher was born in 1953. He arrived with his sister into an affluent and ambitious family during the decade now hailed as the golden era of family life. Years later, his mother, by then the mother of politics, said on television that on the arrival of her twins she had resolved: 'I will not be overcome by this.'

Like the children of their class, these kids were taken into care, so to say -in Britain only the royal, the rich and the dangerous don't take care of their own children. The Thatchers were formal parents. Their babies were brought up by others. That may not have been the worst thing in the world, but in a culture with a rhetoric that was then, and is again, insistent on parents' permanent presence in childhood, Mrs Thatcher's escape was audacious. For years the mega-mother was faking it - she was an absent mother. Of course, no one expected, then as now, that the father would parent these children.

Their tragedy was not that they were entrusted to the collective care of a community of adults but that they were hit by a commandment: thou shalt not disrupt or deflect] They were not welcomed as much as warned that they would change nothing. That is what their mother has told us. She changed the terms of British politics but would not share with other mothers the prospect of a new deal between parents and children.

Her son got into trouble. So do many boys of his generation. The Guardian's Francis Wheen, an old Harrovian contemporary of Mark Thatcher, reckoned many of their classmates are dead, in prison or in disgrace. A Home Office study of crime among children born in 1953 has discovered that a third of the boys had committed criminal offences not connected with drink or driving by the time they were in their thirties. Mark Thatcher is not unusual - getting into trouble is something boys do.

Her friends feared that the boy was bad for her image. But perhaps not: after all, he gave her the opportunity, perhaps for the first time, to be seen as a mother: when he got lost in the Sahara, we witnessed her weeping.

And if their symbiosis is not intimate it is certainly economic. We know that, despite an ideological injunction against state support for British industry, arms dealing attracted enthusiastic government promotion. Mark Thatcher and his rich friend Wafic Said are widely reported to have been couriers during the Al Yamamah arms negotiations in the Eighties. Margaret Thatcher was present, personally, during some of the most dramatic episodes of those negotiations and it is alleged that Mark Thatcher was an emissary between the Saudis and the British prime minister. She is widely reported to have lobbied for Cementation's bid for a building contract in Oman while Mark was a Cementation consultant.

Arms dealing has been one of the few big busineses to attract government interest. Were he to profit from the Al Yamamah deal, and were he to benefit from his privileged access to the Prime Minister, then both mother and son would be open to the charge of corruption. All of this is well known. And if we know that this was dodgy, why didn't they?

The investment in the protection of their reputation has infused even the Opposition: the National Audit Office report on Al Yamamah was never published and the Commons Public Accounts Committee defended its censorship on the grounds that the Saudis might have 'taken amiss at the contents' and anyway the report revealed no corruption by Ministry of Defence staff.

But this controversy does not concern the MoD so much as alleged 'commissions' from the Saudis to a member of the Thatcher family. Any such 'commissions' are not the concern of the audit office or the accounts committee. Their gaze was directed at servants to the Government rather than the head of the Government itself.

Britain's political system has protected Mrs Thatcher's family from scrutiny. The detonator has been pressed outside our borders - one of Ronald Reagan's Security Council experts claims to confirm that Mark Thatcher's role was mentioned in diplomatic dispatches. An exiled Saudi senior civil servant, Mohammed Khilewi, is now reported to have evidence that Mark Thatcher was paid pounds 12m for middlemanning.

After Mrs Thatcher's political demise, her acolytes were concerned that the son would ruin the great mother's reputation. He was bossy and bad-mannered when he took control of the Thatcher Foundation and of her memoirs. But weren't critics missing the point? Mother and son were, by then, each other's greatest assets. And he doesn't have to be a good boy to be a good son. He appears to be doing only what her values obliged him to do: take care of his mother in her old age and take care of business.