The Van Gogh, Picasso and Gauguin watercolours, found yesterday dumped at a public lavatory, were valued at £4 million. When stolen at the weekend, they were hanging together in a room at the Whitworth Art Gallery in Manchester, which houses the Modern Masters collection on the ground floor. They were unscrewed from the wall some time after the gallery closed at 9pm on Saturday.

Initially it was thought that the paintings, the largest of which is 15in by 20in (39cm by 53cm), had been stolen to order, and perhaps spirited out of the country. But the reality is far more intriguing. They were retrieved after an anonymous telephone caller directed police to the back of a disused public lavatory near the gallery.

The paintings were discovered in the undergrowth amid broken bottles and beer cans, rolled up inside a flimsy cardboard poster tube. The frames have not been recovered.

A handwritten note scrawled on the side of the tube suggested that the thieves had carried out the robbery to make a protest. The note is thought to say: “We did not intend to steal these paintings, just to highlight the woeful security.”

Curators for the gallery, which houses one of the world’s most important paper collections, had believed that their security system was tougher than most comparable galleries.

Nicola Walker, the gallery’s paper conservateur, spent several hours painstakingly retrieving the pictures from the tube yesterday. It was the start of weeks of careful assessment and restoration.

The greatest damage is believed to have been caused to Vincent van Gogh’s The Fortifications of Paris with Houses, which was painted in 1878, because one end was protruding from the tube. Pablo Picasso’s Poverty, painted in 1903, and Paul Gauguin’s Tahitian Landscape were safe inside.

A spokesman for Manchester University, to which the gallery belongs, said: “The Van Gogh has a tear in one of the corners, but nothing that isn’t repairable. The other two paintings have been damaged from being exposed to the elements, but all three should be rehung in two weeks.”

The paintings were stolen some time after the audience at a play reading of The Angel and the Fiend, linked to a current exhibition of Lee Miller photographs, had left the building.

Eric Knowles, of Bonhams auction house in London, said: “The person who is trying to make this point has shown total irresponsibility if they have left them outside a public toilet not properly wrapped, and not protected from the elements. I would tar them with the same brush as a common thief.”

Alistair Smith, the gallery’s director, has instigated a review of security. The gallery’s procedures were upgraded in 1999 for The Treasures of the North exhibition, sponsored by Christie’s, which drew together art works in private hands from across the North of England.

The gallery’s collection of 40,000 works is housed inside the distinctive red stone, late 19th-century building. Its ornamental railings have been re- inforced with an 8ft steel chain fence. Exterior doors have been reinforced with steel and iron bars and enlarged windows inviting light into the South Gallery are protected by concertina shutters.

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