The 19-year-old from Rotherham - where the fourth stage started today – produced the best performance of his fledgling career to date.
He said: "It's a fantastic feeling to have the polka dot jersey in my home town and it's something I've dreamed about.
"I thought about it on Tuesday but I never really thought it would happen but I got myself stuck into the break and really enjoyed it.
"This will give me confidence a huge boost. I'm a decent sprinter but I've proved today that I can climb as well and I hope I can keep hold of this shirt for the rest of the week."
Australia's Matt Goss held his nerve in the final kilometre of the third stage of the Tour of Britain to take the win but it was not enough to snatch the yellow jersey from Russia's Nikolai Trusov.
Goss was joined by seven other riders in an early break in the 95-mile stage from Worcester to Wolverhampton and that proved to be decisive.
They opened up a five-minute lead by the halfway point but it was Swift - a Barloworld apprentice - who got most out of the break.
"Going home gave me a bit more of an incentive and it will be a fantastic feeling to go through the Rother Valley with the polka-dot shirt on.
"I was thinking about it on Tuesday night and knew it was going to be really hard but I gave it everything and it worked out for me.
"I've got a decent lead and I will do everything to keep hold of it. Winning th jersey will give my confidence a big boost and it's up to me to make the most of it."