"It was always pretty close with Politt, seven or eight seconds or so, and it was getting tough," said Stannard, who eventually won the stage by 59 seconds.
"Luckily there were a few little kicks towards the end so I managed to put a bit more into the gap.
"When I got into the break today I was pretty confident –- I looked at the other guys, how they were riding all day and I knew that I had the edge."
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Quick-Step Floors rider Alaphilippe is the favourite to defend his green jersey over Sunday's ceremonial final stage in London.
The Frenchman remains 17 seconds clear of Team Sky's Wout Poels after finishing safely within the peloton.
(Reporting by Hardik Vyas in Bengaluru; Editing by Clare Fallon)
