In the end Armitstead's winning margin was 11 seconds over Ashleigh Moolman-Pasio (Cervélo-Bigla), courtesy of three bonus seconds picked up at the day's opening intermediate sprint, with Wiggle HIGH5 rider Elisa Longo Borghini a further two seconds in arrears.
The victory will also move Armitstead up to second in the standings of the UCI Women's WorldTour, behind her teammate Megan Guarnier.
"It means what a fantastic team performance it's been” Armitstead said, "We had quite a lot of pressure on us today with the team performing so well all week I couldn't let them down really so I've relieved and happy that I did it for them.
"It was still hard, although probably one of the easier days of the tour so far which meant we could control it and bring it to a sprint which is what we wanted.
"Being a British athlete I feel so lucky to be a part of a country that loves cycling at the moment and I hope that that bubble continues. My teammates say 'Lizzie, why is it so popular here?' and I don't really know the answer, but events like this certainly help keep the ball rolling.”
A day long breakaway of seven riders contested the finish, as the Boels Dolmans led bunch just misjudged their catch, coming into Kettering 15 seconds behind the group, which Lepistö led home.
The high-class group of seven, including Elena Cecchini (Canyon SRAM) and Marta Bastianelli (Alé Cipollini), built a lead in excess of four minutes, but it was driven down by a combination of Boels Dolmans at the front of the peloton and an eventual lack of cooperation in the front group.
"Today was pretty hard so I went with the break today because my team mate was second in the overall we had to go in the move and finally that move went and we had a pretty big gap and it stayed in the final," Lepisto said.
"I had all the time information in my ear from the manager and he said try to stay calm and sometimes I wasn't allowed to work and just wait for Ashley but in the last 2k it was really close for the peloton to catch us, so then I was confident that I could win the sprint if the break stays
"We worked together this tour, we are really small team but I think we have the biggest hearts the whole week. We started with five and we lost one rider during the week and now the stage win and the second on GC, I think it's pretty amazing.”
Katie Hall of UnitedHealthcare secured the mountains classification jersey while Marianne Vos (Rabobank Liv) took the points classification after a run of consistent finishes, ending each stage in the top five, barring the final day's tenth place.