The X-Files, the cult 1990s television show that made conspiracy theories respectable and gave serious consideration to the influence of aliens on planet Earth, is to make a comeback.

Six years after the series ended on the small screen, the show's creator, Chris Carter, is to release a feature film, the second spawned by the show in the wake of 1998's The X-File: Fight the Future. But, true to the spirit of a show that was always as much about mystery as it was about revelation, the film does not yet have a title, and the film-makers are saying little or nothing about its plotline. The film finished shooting less than two weeks ago and is due out in US cinemas in late July. That much we know.

We also know the film will deal with the six-year period since the television series ended, and offer answers about the mysterious child carried and delivered by Agent Dana Scully, the FBI investigator played by Gillian Anderson, who started out the series as the sceptic assigned to keep an eye on her true-believer partner, Fox Mulder, played by David Duchovny.

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Carter and his co-writer Frank Spotnitz offered these and other clues at a television festival forum in Los Angeles this week, hinting, among other things, that the bitter litigation that pitted them against their paymasters at Rupert Murdoch's Fox empire has spilt over into this project.

Carter said Fox told him the movie had to happen "now or never". A second film was originally supposed to have been made in 2005 (in fact a script was ready from the moment the television show reached the end of its nine-season run) but was scuppered by a lawsuit that Carter filed over syndication rights to the show. That has been settled.

The Fox executives have also clashed with the film-makers over the title. "I know what I want it to be," Carter told the television forum. "But Fox has some ideas of their own." Asked whether the film would give more information about William, the baby mothered by Agent Scully after an apparent close encounter with an alien, Carter said: "It will not go unconsidered in the movie."

The X-Files won 16 Emmys and a Peabody Award. But perhaps more important was the cult status it enjoyed with television audiences across the planet, playing on the age-old American obsession with conspiracies and the paranormal stretching back at least as far as the mysterious 1947 crash in Roswell, New Mexico, which millions of people believe was a botched alien landing.

One of the eeriest scenarios was in the pilot episode of a spin-off entitled The Lone Gunmen, named for three characters in The X-Files obsessed with the assassination of John F Kennedy. In the episode, aired in March 2001, six months before al-Qa'ida struck, the characters try to stop a shady government plot to fly a plane into the the World Trade Centre in New York, although the Bush administration still claims those attacks were unforeseeable. In the episode, the attack was planned to ratchet up military spending and provide an excuse to bomb dictators that the US was itching to topple.