HM Revenue and Customs claimed victory in a tax avoidance battle over schemes run by Ingenious Film Partnership and Icebreaker, worth more than £820m.
The Ingenious scheme tried to use artificial losses arising from backing a range of films, said HMRC.
They included Avatar, Life of Pi and Die Hard 4. The Icebreaker scheme attempted to create artificial losses from limited liability partnerships.
Ingenious called the Tax Tribunal decision "arbitrary and subjective".
"In our opinion, the assumptions on which this conclusion is based reflect an arbitrary and subjective view of future film performance at the moment of greenlighting, and are unreasonable," it said in a letter to investors.
The company said it was "pleased" that the tribunal had recognised the schemes as "bona fide businesses run for profit".
HMRC said both schemes saw users claim more in tax relief than they had invested, something disputed by Ingenious.
It is thought Ingenious will appeal against the decision, contained in a judgement running for more than 300 pages.
The Ingenious scheme members claimed to have financed 100% of the cost of producing films or games.
The bulk of the cost was written off in year one, giving the partners large losses which were set against other income.
But only 30% of the expenditure was actually funded from the partners' cash, the other 70% was routed through the partnership on paper only.
Ingenious said it remained a major investor in film and television, both in the UK and internationally, and said it had recently backed successes such as Brooklyn, Carol and Suffragette.
The Icebreaker scheme members claimed tax relief on losses many times higher than the actual amount they invested in the partnerships.
The return on the partners' "investment" was the tax relief, which was considerably larger than their cash contribution.
Users of the Ingenious scheme were given the opportunity to settle on similar terms nearly four years ago, said HMRC.
They now face big bills for interest on top of the £43m in unpaid tax resulting from the scheme.
The HMRC's decision follows an earlier case in 2014.
The total tax at stake then was £134m, taking HMRC's total in reclaimed monies to more than £1.2bn.
Jennie Granger, Director General of Enforcement & Compliance, HMRC, said: "These were some of the biggest films of all time, and the schemes involved people claiming far more in tax than they invested in the first place.
"We always say that if something is too good to be true then it probably is. And in this case, the long legal battle will mean that investors face even bigger bills."
However, Neil Forster, Ingenious CEO, said: "HMRC appears to be deliberately confusing the Ingenious case with other proven tax avoidance schemes and making assertions which are factually wrong. The Ingenious investors received no more tax relief than the cash they invested."