Armitstead – now Lizzie Deignan – led an England one-two ahead of retiring team-mate Emma Pooley in an exciting women’s race.
Pooley, in her last race before switching to endurance triathlons, played a brilliant selfless role in the 98-kilometres event – seven laps of a 14km undulating course – and finished with silver as 25-year-old Armitstead triumphed.
“I just feel like I deserve it,” said the Otley rider, who claimed silver behind Australia’s Rochelle Gilmore in Delhi four years ago and secured Britain’s first medal of London 2012 – with Olympic silver – behind Marianne Vos of Holland.
“I’ve trained so hard. I’m always on the podium, I don’t win that many races.
“It’s just a confidence thing. Once you’ve got a big title, you can call yourself a champion finally.”
England finished top of the medal table with 174, 58 of them gold.
Thomas won gold for Wales in the men’s discipline, triumphing in torrential rain in a race which became about survival and brute strength.
The 28-year-old from Cardiff, fresh from finishing the Tour de France a week earlier, twice suffered front-wheel punctures, including in the last six kilometres as his rivals neared.
But Thomas soloed to victory by one minute 21 seconds as Jack Bauer of New Zealand beat England’s Scott Thwaites to silver, the Yorkshireman having to settle for bronze.
“Riding the Tour before, it just adds to how good it feels to come away with two medals. I really didn’t expect it,” said Thomas, who also took bronze in the road time-trial.
“I was coming purely out of national pride and wanting to ride for Wales. I never really expected to medal, if I’m honest.
“To come away with a win and a bronze is more than I could’ve dreamt of.”