Yet to listen to some on the Labour benches, among the higher reaches of the Ministry of Defence and in the boardrooms of Britain's biggest defence manufacturers, you would think he was their number one bogeyman.
Mention his name and a torrent of bile emerges: dangerous, sinister, far right, upstart, CIA links, determined to slash the armed forces, friend of US defence contractors, eminence grise to Michael Portillo.
Last week, Labour was at it again, with the party's defence spokesman, David Clark, using the occasion of the defence debate to challenge Mr Portillo about the security clearance of his close friend - or to give Mr Hart his official title, "independent adviser."
Following the debate and Mr Portillo's stoic refusal to be drawn, a series of parliamentary answers forced out of the Secretary of State for Defence by Labour have shed some light on his role.
"Mr David Hart is currently providing advice to me on the following equipment projects: EF 2000, Astor, Phoenix, Tornado F3 Upgrade and Long Range Conventionally Armed Stand-Off Missile." Plus, said Mr Portillo, he had also discussed "various aspects of the situation in the former Yugoslavia with Mr Hart".
Not a bad list for someone who has never worked in the defence industry, never fired a gun on active service and spends most of his time developing property and farming his estate in Suffolk.
And despite the hard-nosed instinct for a deal he has shown in the past, his valuable services to government come for free. As he insists: he serves Mr Portillo, and before him, Malcolm Rifkind, out of a sense of duty and love for his country, nothing more, nothing less.
According to Mr Portillo, his friend has a pass for the MoD and is subject to the provisions of the Official Secrets Act. "In addition, he owes me a personal duty of confidence." As for any possible conflict with his private interests, Mr Portillo declared that the onus was on Mr Hart to declare it.
Such freedom for one with undoubted access to affairs of enormous commercial and strategic confidentiality is unheard of, say those close to the MoD. It is precisely because he is a close friend and he is working for nothing, they say, that such latitude is tolerated.
Fuelling the air of mystery, Mr Hart, for all his bluff exterior, doesn't give much away. He does not appear in Who's Who and he does not give interviews. He is an Old Etonian who inherited a fortune from his father, the founder of the financiers Henry Ansbacher, and first shot to public prominence when he popped up advising Ian MacGregor on the 1984 miners' strike. He was chairman of the Committee for a Free Britain, a right-wing pressure group, and once ran an agency publishing Russian dissidents' work in the West. Beyond that, few hard facts are known.
The listing of his businesses at Companies House is a textbook case in how to comply with the law and make all the right declarations, without saying much at all. He is 51, lives at Chadacre House, near Bury St Edmunds, and is at present a director of 15 companies. Several are property vehicles set up to develop parcels of land or office blocks in a town or city, so you have Arcadia Land (Cambridge), Arcadia Land (Liverpool) and Arcadia Land (Amersham).
Some appear less conventional. One was called Gorky Park Developments Limited. Another, Federal Aviation, is in the aircraft business. Most of them take full advantage of the rules governing limited disclosure and say nothing about their sales and profits figures.
Their registered offices are frequently given as an address in Finchley Road, north London. Ownership of one of them, Marathor Properties, is concentrated in the impenetrable British Virgin Islands.
Two articles in the Spectator magazine have come to be seen as declarations of policy. One argued that if Britain intervened in the former Yugoslavia it should be to back the Serbs. The other discussed the shortcomings in British armed forces and procurement programmes - in particular, questioning the EF 2000 Eurofighter project and the Vickers Challenger II tank.
One tale clearly illustrates the problems of dealing with Mr Hart. During the battle to win the army attack helicopter, Westland, which owns the Battersea Heliport, became concerned about landing and take-off fees owed by Mr Hart. The company did not know what to do. Should it contact him and risk upsetting the prospects for its bid, or should it say nothing and risk being accused of favouring him. After much hand-wringing, he was contacted and the money paid. Westland need not have worried - they got the order.
For Labour, Mr Clark asked yesterday: "What qualifies [Mr Hart] to advise on multi-billion pound, very high-tech, sophisticated weapons contracts?"
The Liberal Democrat defence spokesman, Menzies Campbell, yesterday wrote to the Prime Minister: a damaging proposal to British industry that the RAF should lease US F-16 aircraft required Mr Major's personal intervention. The plan appeared to have emanated from Mr Hart - but, as ever with Mr Hart, Mr Campbell could not be sure.Reuse content