The former engineer, turned photographer, then entrepreneur had been due to stand trial on Monday over the 1988 collapse of Lancaster-based company Africar International in the latest prosecution by the Serious Fraud Office.
The collapse left creditors in the lurch to the tune of pounds 1.5m and stranded investors, many of whom had been attracted by a six part Channel 4 series in 1987, which featured Mr Howarth driving the concept car on a 6,200 mile trek from the Arctic to the Equator.
Mr Howarth was in the US at the time of the crash, then disappeared, only to return in October 1994 to give himself up to Lancashire police, SFO sources say.
Sentencing has been deferred to 20 June at Liverpool Crown Court and the theft and Companies Act charges carry maximum sentences of 10 and seven years respectively.
Africar's collapse marked a sad end to Mr Howarth's perhaps unrealistic eight-year quest to build a whole series of affordable, rough terrain cars after his experience of driving thousands of miles along dirt tracks in Africa.
The vehicle, looking like a cross between an armoured car and a modern Japanese 4x4, was to made from plywood soaked in epoxy resin on a chassis that owed much to Henry Ford's Model T.
A specially designed two-stroke engine aimed to cut moving parts - and vulnerability to breakdown - to a minimum.
Africar's pilot factory in Lancaster was set up in July, 1986 to build 250 sample vehicles initially and 5,000 a year in full production. Under ambitious expansion plans, 20 further plants were to be set up around the world, using 60-90 per cent local content to boost local economies.
Africar's ownership followed more modern financial planning, with control resting with a Dutch foundation, the Worldwide Appropriate Transportation Trust.
In 14 original charges, the SFO alleged Mr Howarth fraudulently obtained monies from investors and customers from Africar's start to finish, knowing that the company could not make the car and fulfil the ambitions trumpeted in its publicity.
In the about-face last week, Mr Howarth pleaded guilty on just six counts, admitting trading while he knew the company was in trouble from the start of 1988 onwards. Five counts of theft were admitted, all relating to customers who placed orders in March and April that year, that could not be fulfilled.
After plea bargaining, the SFO dropped the remaining charges.
"It always has to be balanced. What a defendant pleads guilty to and the cost of a trial. What he has pleaded guilty to is a fair reflection of the charges against him," the SFO said.