Telefonica is in talks with billionaire John Malone's Liberty Global to explore a merger of its British mobile operator O2 with Liberty's Virgin Media cable network company, the Spanish company said on Monday.

A combination of O2 and Virgin Media would reshape Britain's telecoms industry, leaving Hutchison's Three and Vodafone stranded without their own fixed-line consumer networks and increasing the pressure on BT.

Here is a look at the big players in UK mobile telecom and broadband:

MOBILE OPERATORS:

* O2 Mobile: Telefonica UK, which includes the O2 Mobile business, had 34.5 million customers at the end of 2019, with revenue of 7.1 billion euros ($7.8 billion).

* BT's EE: The telecom operator provides mobile, fixed and wholesale connections to about 31 million customers, according to its website https://ee.co.uk/our-company/about-ee.

* Vodafone: Vodafone had 17.2 million UK subscribers as of Dec. 31.

* Three, controlled by CK Hutchison Holdings, has more than 10 million active customers in Britain.

* Virgin Mobile: Virgin Mobile had 3.2 million subscribers as of the end of last year with revenue of 656 million pounds.

Virgin Media pioneered the mobile virtual network operator (MVNO) model, whereby a company offers own-branded mobile on an established partner's network.

Virgin Mobile currently piggybacks on BT's EE network. It had signed a five-year deal to switch to Vodafone's network from late 2021.

BROADBAND:

* BT: BT had 12.2 million fibre broadband customers, according to its latest annual report. The company's share of total fixed broadband connections was 34.1% in the third quarter of last year, according the UK's telecom regulator.

* Virgin Media: Virgin Media provided cable broadband internet services to about 5.3 million subscribers in the UK, as of Dec. 31.

* TalkTalk Telecom: TalkTalk has 4.3 million broadband customers.

* Sky: Owned by U.S. media group Comcast Corp, Sky had 23.9 million retail customer relationship, as of March 31, including internet, voice, wireless phone services, broadcast, sports networks, among others.

Sky and BT are the dominant players in sports broadcasting in Britain.

Source: Company reports, websites, Ofcom report https://www.ofcom.org.uk/__data/assets/pdf_file/0020/190442/q3-2019-telecoms-data-update.pdf

(Reporting by Yadarisa Shabong and Pushkala Aripaka in Bengaluru; Editing by Keith Weir)