In the first case of its kind, Mr Thomas upheld the UKAEA's refusal to hand over seven files to Edinburgh-based environmental journalist Rob Edwards. Mr Thomas claimed disclosure could have "a far-reaching impact on the national security of the UK".
Mr Edwards had sought information relating to fissile materials held at the UKAEA's defunct fast-reactor site. After having his initial request knocked back in March 2006, he used Freedom of Information legislation in a bid to force the UKAEA to hand over the data.