This song has been driving me crazy ever since I first heard the commercial, and I finally found it! The song is performed by Gin Wigmore from New Zealand called "Don't Stop" from her album "Holy Smoke".
That's Ann Wilson of the band Heart (sister Nancy can be heard singing harmony near the end). That's not part of a song otherwise published or available anywhere so the assumption is that it was recorded specifically for the commercial.
Solsbury Hill is the name of the song. I'm not sure who's actually singing it in the commercial because I've heard different versions. Peter Gabriel sings the original version. Erasure did a cover, but somene else may be singing it in the commercial.