A more detailed report here suggests that the fire started in a chimney: http://www.bbc.co.uk/news/uk-england-norfolk-30609946
Our house had a very similar near miss about 20 years ago. Family gathering for Christmas . . . open fires lit beneath seldom used chimneys . . . flues full of twigs dropped down by nesting birds . . . resulting chimney fire apparently burned out safely . . . two days later, chimney breast still warm and paint beginning to discolour . . . . fire brigade called and opened up the plaster to investigate whereupon flame erupts from the remains of the 9x6 inch oak bressummer, which had almost completely smouldered away. Fortunately, the resulting small fire was very localised and easily dealt with, causing no further damage - but had everyone been out that particular evening when the fire was about to break though the wall . . . . well, who knows?