A dad has faithfully restored a nuclear bunker that was once used to monitor for radioactive explosions across Britain.br br Jon Graves, 37, reinstated the 15ft-deep ex-Royal Observer Corps pit so he could preserve the piece of British Cold War history.br br The fallout shelter - which was manned by observers from 1964 to 1991 - was capped off with concrete when he bought it three years ago.br br But after the dad-of-three finally broke into it, he discovered that the underground military-grade hide-out had remained remarkably intact.