Cummings took advantage of Vermote’s struggles but trying to join Poels and the stage leaders, eventually finishing the stage 20 seconds behind Poels to take an advantage of 49 seconds into the final three stages.
Tom Stewart (Madison Genesis) was the sole British rider in the day’s four-man breakaway, mixing it with WorldTour rider Giovanni Visconti (Movistar), intermediate sprints leader Jasper Bovenhuis (An Post Chain Reaction) and Miguel Angel Benito (Caja Rural)
Bovenhuis was the first to crack with 45km to the line and Visconti decided to go off on his own with 21km to go – a move that lasted 10km or so with Team Sky powering hard on the front of the peloton.
Danny van Poppel put a huge turn in on the front in the final 10km, looking to set up Poels or Irishman Nicolas Roche for the stage win.
Bardiani CSF’s Edoardo Zardini attempted to up the pace with five kilometres to go, but was joined and passed by BMC’s Rohan Dennis. Tom Dumoulin (Giant-Alpecin), Gorka Izagirre (Movistar) and Poels sensed the danger and attempted to bridge to Dennis.
Yellow jersey holder Vermote began to struggle with three kilometres still to go on the climb, with Etixx-Quick Step changing their focus to Dan Martin, who sat fifth overall before the stage.
Second-place man Cummings (Dimension Data) made his move with 2,500m to go, having seen his nearest rival Vermote fade away. Cummings needed just six seconds to overtake Vermote, but with dangerous riders up the road the Wirral man couldn’t allow the breakaway go get away.
Dumoulin, Poels and Dennis made another jump to distance Cummings and the Team Sky man dummied before speeding off in search of the stage victory.
Dennis and Dumoulin dug deep in hope of catching Poels, but the Dutch rider had enough of a lead to stay away up the steep finish of Haytor and take Sky’s second win of the week.
Saturday sees riders enjoying a double day, with a 15km time trial taking place in Bristol in the morning before a 90km criterium following on the same course in the afternoon.
Tour of Britain stage six, Sidmouth – Haytor (150km)
1. Wout Poels (Ned) Team Sky, 4-56-15
2. Rohan Dennis (Aus) BMC, at 6s
3. Tom Dumoulin (Ned) Giant-Alpecin, at 10s
4. Dylan van Baarle (Ned) Cannondale-Drapac, at 12s
5. Xandro Meurisse (Bel) Wanty-Groupe Gobert, at 16s
6. Nicolas Roche (Irl) Team Sky, st
7. Tony Gallopin (Fra) Lotto-Soudal, st
8. Steve Cummings (GBr) Dimension Data, at 20s
9. Erick Rowsell (GBr) Madison Genesis, at 30s
10. Gorka Izagirre (Esp) Movistar, st
Overall standings after stage six
1. Steve Cummings (GBr) Dimension Data, 27-04-11
2. Tom Dumoulin (Ned) Giant-Alpecin, at 49s
3. Rohan Dennis (Aus) BMC, at 51s
4. Tony Gallopin (Fra) Lotto-Soudal, at 53s
5. Dylan van Baarle (Ned) Cannondale-Drapac,
6. Xandro Meurisse (Bel) Wanty-Groupe Gobert, at 58s
7. Nicolas Roche (Irl) Team Sky, at 1-06
8. Ben Swift (GBr) Team Sky, at 1-14
9. Jacopo Mosca (Ita) Trek-Segafredo, at 1-20
10. Guillaume Martin (Fra) Wanty-Groupe Gobert, at 1-24