Dr Robin Catchpole (RGO) and Dr Don Cowan (UCL) welcome the news

A dual observing session is now underway, linking the huge dish at Arecibo, Puerto Rico and Jodrell Bank, Cheshire, UK.

The first attempt to do this failed last autumn after Hurricane George damaged the Arecibo dish, requiring two months of repair work.

The Lovell telescope could detect a mobile telephone 220 million miles away

Two sessions are planned every year, each three weeks long. Dr Ian Morison, the Jodrell Bank co-ordinator, told BBC News Online this would mean over 1,000 selected stars could be targeted in the next three or four years.

"We are looking Sun-like stars within a distance of 200 light years from Earth," says Dr Morison.

"Astronomers expect that other civilisations are most likely to be found on planets in orbit around stars similar to our Sun. Such stars live long enough and provide enough heat to allow life a chance to evolve."

Millions of channels

Arecibo hosts multi-million channel receiver, started by Nasa and now supported by the privately-funded Search for Extra-Terrestrial Intelligence (Seti) Institute, in California. It searches a wide band of radio frequencies for extra-terrestrial signals.

Radio waves are favoured because they travel relatively unhindered through space and are easy to detect.

The 76m Lovell telescope at Jodrell Bank receives commands from Arecibo so that both are looking at the same star. This is crucial, as it is the only way to rule out "false alarm" signals originating from terrestrial or satellite interference.

The two telescopes are thousands of miles apart, so only signals from beyond the orbit of Jupiter can trigger the detection system in both places at the same time.

The detector antenna at Arecibo hangs over the dish

The astronomers spend an hour at the start of each observing session making sure that this "double-check" is working. They do this using the signal from the 26-year-old Pioneer 10 spacecraft, now beyond the orbit of Pluto.

This safety check is unique in Seti science, says Dr Morison, as is the real-time analysis of the incoming data: "We would know if we had something within 10 minutes."

A separate project at Arecibo, Project Serendip, taps information from the telescope when it is performing other astronomical observations and analyses it later.

The 305m-diameter dish at Arecibo appears in the James Bond film, Goldeneye. Thanks to special effects, the main antenna appears to crash 100m to the floor of the dish.