The two-day festival, which takes residence on Clapham Common over the bank holiday weekend of August 29-30, also revealed Kelis and Stefflon Don as its afternoon headliners.
Rudimental will host the indoor main stage on the Saturday, with special guest DJ EZ. On Sunday, Andy C, Example, Ms Banks and more will appear.
Elsewhere, there will be performances from Ghetts, Steel Banglez, Eli and Fur and others.
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How to get tickets for South West Four 2020
Pre-sale tickets will go on sale at 9am on Thursday 23 January, with general sale commencing at 9am on Friday January 24. Buy tickets here.