By Ed Chatterton & Rom Preston-Ellis A teacher was left stunned after digging up a stone carved with an ancient Celtic script dating back to the 4th Century while weeding in his garden – in Coventry. Graham Senior, 55, had been clearing out his overgrown flowerbed when he made the incredible discovery during lockdown in May 2020. It has since emerged the sandstone rock bears an early form of Ogham script from Ireland – dating back around 1,600 years. The 11cm (4ins) stone has now gone on display at a museum while experts try to figure out the full meaning of the mysterious relic. The rectangul…