The mobile carrier plans to acquire UK Broadband in a transaction valued at £300 million ($373 million) - with £250 million being paid up front, and "a deferred £50 million "made available as a credit toward an MVNO agreement on Three's network".
CK Hutchison subsidiary Three UK has agreed to buy UK Broadband Limited from PCCW for £250 million.
UK Broadband, which switched on the country's first commercial 4G network in 2012, is owned by Hong Kong-based IT, media and telecoms group PCCW.
Shares of PCCW rebounded on Tuesday for the first time in four trading days in Hong Kong, after the company announced a 300 million-pound ($373 million) deal to sell a United Kingdom broadband business.
Three CEO Dave Dyson said the deal was a good move for the firm to help it broaden its portfolio of offerings.
UK Broadband Ltd provides broadband access via a combination of licenced spectrum and fibre backhaul.
Three UK is a communications company focused on making the industry better for everyone.
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"Three remains in a precarious position as a mobile-only provider in a United Kingdom market rapidly evolving to multiplay services", he said.
Three, which has been openly critical of United Kingdom regulator Ofcom, has called for spectrum caps as part of the Make the Air Fair campaign it launched past year alongside rivals including Relish.
Since it is so recent, it stands to reason that it is also the most data-forward: today, its network carries 35% of the UK's mobile data traffic.
"UK Broadband was nearly certain to take part given its aspirations to expand its service beyond London, Swindon and Reading", he said.
Kester Mann, principal analyst at CCS Insight, pointed out that much of the new spectrum being acquired by Three will not be compatible with most of today's mobile devices, which means it can not be put to immediate use.
Three will also get access to UK Broadband's spectrum holdings, something that will prove invaluable for delivering 5G services in the future.