The actress was at Blair Athol Distillery in Perthshire to begin the Bell's Barrel of Laughs - a 517-mile (832km) celebrity barrel rolling relay to raise money for Help for Heroes.
Personal trainer Rod Edmond aims to roll the large wooden barrel through the streets of the UK over the next nine days on a route to the Help for Heroes recovery centre in Tedworth House, Wiltshire.
He will be joined by veterans and comedians each day, including Fred MacAulay, Mark Dolan and Rufus Hound, who will help roll the barrel and stage free stand-up gigs at pubs along the route.
Lumley was joined by military veterans and staff from the distillery to start the barrel rolling this morning.
She said: "I feel so proud to have been chosen to start the great Barrel of Laughs journey for Help for Heroes.
"Full marks to Bell's for such a generous and brilliant idea and all praise to everyone concerned with Help for Heroes. We shall never forget the duty of care we owe to those who have been damaged in conflict for our sakes and the sakes of our country.
"If this were Patsy speaking, she would say 'Cheers, sweeties'."
Fitness expert Edmond, who was the personal trainer on ITV's The Biggest Loser, will roll the barrel for 12 hours a day on the journey from Blair Atholl to Tedworth House.
He said: "It's going to be a physical and mental challenge rolling the barrel 517 miles across the length of the country but we're all determined to make it happen and I'm sure the banter will keep us all smiling right until the finish line."
The first stage of the challenge is between Blair Athol and Edinburgh Castle and it will later pass through Newcastle, Leeds, Manchester and Birmingham.
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