The track is being released as a double A-side with new song 'The Puritan' via Parlophone on August 6 after both songs are live streamed via Twitter.
'Under The Westway' will be performed at 6.15pm on July 2 and followed by an exclusive interview with the band, before 'The Puritan' is performed at 7.15pm.
Watch Alex James announce Blur's new songs below:
'Under The Westway' was performed by frontman Damon Albarn and Graham Coxon ahead of this year's Brit Awards during a live show at the O2 Shepherd's Bush Empire in London.
The band play London's Hyde Park on August 12 with support from New Order, The Specials and Bombay Bicycle Club.
Albarn has suggested that the gig could be the band's last, though he later said that the band is not finished.
Watch Damon Albarn and Graham Coxon performing 'Under The Westway' below:
Watch Damon Albarn perform 'The Puritan' below: