It is the most eagerly awaited finale to an American television show since The Sopranos: the episode that will determine the fate of Walter White, the mild-mannered chemistry teacher turned gun-toting drugs kingpin.

Nor is it an ordinary TV series: the five series saga of a man with cancer, played by Bryan Cranston, who attempts to secure his family's future by using his talents to make a fortune out of producing a high quality version of the drug crystal meth has played with viewers' sympathies in a way that few other shows have dared.

Last broadcast on a traditional UK television channel more than two years ago, former X Files veteran Vince Gilligan's creation had barely a million viewers when it first screened in the US.

But it built its reputation by word of mouth and on social networks on both sides of the Atlantic.

UK viewers scrambled to catch up with box sets, illegal downloads and – since its launch in this country last year – via the video on demand service Netflix, which will unveil the final episode at 9am on Monday, a few hours after it is broadcast in the US. In the US, earlier episodes of the fifth and final series have attracted more than 6 million viewers, making Breaking Bad one of the most popular shows on cable TV.

Such is the level of secrecy around the finale that even senior executives at Sony, the producer, do not know the ending. Leading actors shot their scenes separately where possible, and several different endings were filmed for security.

Keith LeGoy, president of international distribution for Sony Pictures Television, said: "What we have seen is this amazing convergence of technology and storytelling that has enabled a global community to find each other and discover the show".

Netflix, which made Kevin Spacey's acclaimed $100m (£62m) drama remake House of Cards, prides itself on allowing viewers to "binge watch" by making all the episodes of a series available at the same time. Except Breaking Bad, which is broadcast in the US on Sunday nights by cable and satellite channel AMC.

"It is one of the ironies that Netflix, which has built its business on the basis that you can access this vast bulk of content, is here behaving much more like a traditional broadcaster. They have embraced it, and made it into a virtue," said LeGoy. US-based Netflix has about 1.5 million subscribers in the UK and a worldwide customer base of 38 million, but refuses to disclose viewing figures.

However, in the absence of official ratings, online statistics give an alternative indication of the show's popularity: there were nearly 7 million mentions of #BreakingBad (or plain old "Breaking Bad") on Twitter since its returned for the second half of its fifth series last month.

Sold to more than 170 countries worldwide (and remade in South America as Metastasis), the show is one of the top 20 most searched for phrases on Google.

So concerned was Netflix that viewers might have their enjoyment of the show spoiled on Twitter that it launched a "spoiler foiler" purporting to black out "danger words" related to the show from tweets.

Gilligan has already moved on. He has two new projects, one a detective drama called Battle Creek, which he is making with House showrunner David Shore, and a Breaking Bad spin-off, Better Call Saul, a prequel based around the drama's shady, wise-cracking lawyer, Saul Goodman.

But fans hoping for a sequel of sorts to Breaking Bad are likely to be disappointed: "The two will have a relationship and a linkage creatively but I don't know they are that closely connected," said Gilligan, who famously pitched Breaking Bad as "Mr Chips turns into Scarface".