Duncan Davidson, chairman of Persimmon, Britain's third-largest housebuilder, is constructing the tracks to link his growing number of grouse moors in the Cheviot hills.
The development has concerned some Northumberland National Park officials, who fear it may impair the remoteness and unspoilt peace which are the park's special qualities.
Mr Davidson's plan is to construct three tracks leading up the sides of one of the prettiest valleys, Harthope.
He has been constructing the tracks, with mechanical diggers, to link up the various moors and make vehicle access easier.
They are often referred to locally as roads, but are described as tracks on planning documents, in line with Mr Davidson's view. "With respect, I'm the guy who's building them, and they are hill tracks," he said.
However they are described, all are within the boundary of the Northumberland National Park and officers are concerned that they do not accord with the park's purpose.
"This is a very difficult issue," said Terry Carroll, the deputy national park officer, and the official in charge of planning. "Here is unspoilt moorland with bags of the national park's special qualities, remoteness, lack of development, tranquillity, seemingly a wilderness - and you introduce a road. Or you introduce a network of them, which are more or less conspicuous.
"What effect does that have on the special qualities?
"People who go there for unspoilt solitude are certainly going to have their view impaired."
Mr Davidson's estate has already been brought to the attention of park officials over 14 kilometres of tracks which have already been built. Two were constructed without proper notification, and another was built bigger than the specification suggested.
Mr Davidson is planning three more tracks, rising out of the Harthope Valley, celebrated by writers including Daniel Defoe and Sir Walter Scott.
Park officials consider the Harthope Valley tracks, totalling eight kilometres, to be for grouse moor management, and therefore asked for full planning applications, which farm and forestry tracks do not need.
Mr Davidson has received planning permission for all three from the National Park Authority, although Mr Carroll and his officials had suggested that one of the applications should be refused. But he has failed with his application for a fourth track, which would have penetrated the wild country under The Cheviot, the 2,600ft peak of the range.
Mr Davidson, 57, is not only the largest private landowner in the park, with more than 25,000 acres - most of the Cheviots now belong to him - but he is also one of the richest men in Britain. His personal fortune was estimated this year at pounds 60m, but some sources put it at more than pounds 100m. He is blue-blooded into the bargain, being the nephew of the last Duke of Norfolk, at whose side he assisted as a page boy in the Coronation in 1953.
Despite his wealth, power and connections, Mr Davidson has succeeded in keeping an extremely low profile. He is unknown as a public figure outside the world of finance. Newspaper references to him are limited mainly to the booming Persimmon's annual results. There is not a word about him in Who's Who.
His reticence has kept from public view a remarkable social phenomenon: at a time when many large land holdings are being broken up and sold off piecemeal, Mr Davidson has been building up a great country estate, to rival that of his near neighbour, the Duke of Northumberland.
For the past decade he has been steadily buying moorland farms in the Cheviots, at a cost of millions of pounds, and reducing the numbers of sheep to bring back the heather. This provides much better conditions for grouse, country sports and shooting, which are Mr Davidson's passions.
Mr Davidson said he saw nothing in the tracks to which anyone could take exception.
"It's a very large area of land, and it's also a fairly large-scale working sheep farm," he said.
"We need to get around the place and we have very bad weather in winter.
"It's only what's required for the various enterprises on the estate, sheep farming, forestry and so on.
"I own all the land in question and I've been a countryman all my life. I certainly don't feel any of the work we're planning to do to put in these tracks is going to impair the environment at all."