"Prospero was the first UK satellite to be launched on a UK launch vehicle; it would also be the last. Ministers had cancelled the rocket project in the run up to the flight. However, as the Black Arrow was ready, the programme team decided to go-ahead anyway. Prospero was blasted into orbit from the remote Woomera base in the Australian desert. It turns out, the satellite is still up there. Carrying a series of experiments to investigate the effects of the space environment, the satellite operated successfully until 1973 and was contacted annually until 1996. Now, a team led by PhD student Roger Duthie from University College London's Mullard Space Science Laboratory in Surrey is hoping to re-establish communications in time for the satellite's 40th anniversary. "First, we have to re-engineer the ground segment from knowledge lost, then test the communications to see if it's still alive," Duthie told the Space Boffins podcast." More at the BBC
According to Wikipedia "As of 2006, radio transmissions from Prospero could still be heard on 137.560 MHz, although it had officially been deactivated in 1996, when the UK's Defence Research Establishment decommissioned their satellite tracking station at Lasham, Hampshire. It is in a low Earth orbit, and is not expected to decay for about 100 years."