Merrien had previously won the British singles title five times and had pocketed the pairs three times – but this year she went one further by winning both titles on the same day.
Before lunch, she saw off the skilful challenge of one of the most promising young women players on the UK scene, beating Ireland's 17-year-old prospect, 21-11, in the singles final.
Then, in the afternoon, she was joined by the ever-reliable Shirley Petit, and the Guernsey duo played superbly to retain the pairs title they won last year, again accounting for Irish opposition in the form of Belfast's Cliodhna Eadie and Sandra Bailie, 23-14.
'I obviously wanted to win both titles, but didn't really allow myself to think about it, because it might have been a case of tempting providence,' said Merrien last night.
'I preferred to take the finals one game at a time – but it's a great feeling to have done the double.'
More in Thursday's Guernsey Press.