BBC News' Stephen Cape reports from the trial

John Drewe, 50, was convicted of conspiracy to defraud, two counts of forgery, one of theft and one of using a false instrument with intent. He was acquitted of one other charge of forgery.

Drewe, who defended himself in court, was accused of using deception to gain access to valuable art archives - including those at the Tate Gallery and the Victoria and Albert Museum. He then created bogus backgrounds about works he had commissioned.

He claimed his fake paintings were newly rediscovered works and amassed up to £1.8m in the process by selling them.

Drewe even donated £20,000 to the Tate, leading officials to trust him as a "serious researcher."

He appeared with artist John Myatt, 53, who admitted conspiracy to defraud, at Southwark Crown Court in London. They will be sentenced on Monday.

Drewe made a £20,000 donation to the Tate

Drewe's co-accused Daniel Stoakes was acquitted of conspiracy to defraud at the end of the four-and-a-half month trial.

Mr Stoakes said although he had posed as an art seller, he had believed that everything Drewe asked him to do was legal.

Prosecutor John Bevan QC said Drewe's primary motive was to make money but the effort he put into the deception suggested "an intellectual delight in fooling people and contempt for experts".

Mr Bevan spoke of the damage Drewe had done by putting fakes into the Tate and V&A's archives.

"Corrupting such material damages not only the individual item, but inevitably undermines and taints the whole system," he said.

Both institutions have since reviewed their security after trusting Drewe, who had been operating his scam for 10 years.

Waste of 'astute brain'

But Mr Bevan also said it was a shame that Drewe chose to use his talents for fraud.

"It was a waste of a clever, astute, hugely retentive brain." he said. "He has wasted himself on a lifestyle which has left a trail of victims in its wake."

One suspected fake, which was said to have been described as a genuine work by British painter Ben Nicholson, was reportedly sold for £105,000 ($175,000) in the US.

Drewe also managed to fool Sotheby's and Christie's, which unwittingly found buyers for some of the fakes.

Jelly, varnish and dust

Seven of the fakes were exhibited in court opposite the jury.

They included two pastiche Sutherlands, including one Drewe said was a preliminary sketch for the modern master's famous Coventry Cathedral tapestry of Christ and the Apostles.

Others were supposed to have been by Alberto Giacometti, Roger Bissiere and Nicholas De Stael.

Drewe and Myatt used a variety of household goods to age their paintings. Drewe made frames out of old wood and nails which were rusted with a salt solution.

He used a book of artists' signatures to forge the one he wanted.

Myatt used a concoction of common household emulsion, lubricating jelly, varnish, vacuum cleaner dust and mud to give his paintings a more weathered look.

Jury praised

The trial lasted almost six months, which was much longer than had been expected. Judge Geoffrey Rivlin QC described the case as "extraordinary" and the Crown Prosecution Service said it was "unique".

Judge Rivlin congratulated the jury on their "extraordinary attention", which he described as "quite remarkable".

"Please don't think I don't understand how much inconvenience has been involved for you all," he said.

"The best reward I can give you is to excuse you from jury service for life."