The mysterious sealed box marked 'transmitter' found in a war shelter in a hairdresser's garden was opened yesterday, revealing a jamming device that could today 'wipe out most television in the area'.

The wooden crate was found in a second world war Anderson Shelter, by hairdresser Kirsty Pope, 30, at her salon Hair to Impress, on St John's Close in Norwich.

She told the Evening News last week that she was 'very curious' about what was inside the box, which is marked 'not to be opened until required for use'.

A stamp on the box states its last charge was September 14, 1951, six years after the war ended.

Yesterday, Miss Pope's father, Michael Pope, an insurance assessor, and Steve Appleyard, a volunteer at the Muckleburugh Military Museum in Weybourne, peeled open the box to reveal a T1951 radar – also known as the T-39/ARQ-9.

Mr Appleyard, former head of navigation systems at the Marconi Company in Chelmsford, said the radar would have been carried on British and American planes as they flew over Germany during the second world war.

Their sole use was to disable the German Wurzburg radars, which helped the German gun aim.

He said: 'The transmitter sweeps across frequencies that are now used for television, so if it was switched on today it would wipe out most television in the area.'

Miss Pope said: 'Now that it's open I just can't believe what a brilliant condition it's in.

'I never expected that inside there would be something that looks so new.' She added: 'There is no point in packing it up and putting it in the attic. We may as well give it to a museum.'

Mr Pope, 57, said: 'We can't believe how long it's been down there and no one has found it until now.'

It's thought there were a total of 4000 manufactured, with a range of 43 miles, reaching a frequency of 450-500 MHz.

Mr Appleyard said: 'To anyone interested, this is quite an exciting find.'

Evening News readers emailed their thoughts on the box.

One, Chris Jones, said: 'We are all waiting with baited breath as though an Egyptian mummy was about to be unwrapped.'