In two years of operation, BritBox has snagged more than 650,000 subscribers in North America with its “best of British” lineup of drama, soaps, unscripted shows and live programming. Now that it’s lifted the lid on its plans to launch in the U.K. later this year, the question for co-owners ITV and the BBC is whether the service will succeed on home turf, where Netflix – which faces losing “The Office,” “Sherlock,” and “Love Island,” as the BritBox owners take back their shows – has already made inroads.

The international version of BritBox is a joint venture between ITV and BBC Studios. At home in Britain, ITV has more skin in the game with a 90% stake; the launch is a key part of CEO Carolyn McCall’s plans for Britain’s biggest commercial broadcaster. Pubcaster BBC will not fork over any cash for its 10% share, but has the option to invest money to boost its stake to 25%.

Brits are now seasoned SVOD streaming customers, but BritBox will be one of an increasing array of choices. “They’re saying the right things: British content focus, binge viewing, original shows,” said Ed Barton, chief entertainment analyst at London-based Ovum. “But there are a lot of questions, and it will be launching into a very competitive market for subscription video services in the U.K. I’m also a little surprised at how much the initial share split favors ITV. Starting with a 10th of the venture, how aggressively is the BBC incentivized to make Britbox work?”

Ratings agency BARB estimates that, as of the end of March, there were 13.3 million overall SVOD subscribers in Britain. Netflix had an estimated 11.5 million, Amazon about 6 million and Sky’s NowTV about 1.6 million. (Many Brits subscribe to more than one service.) BritBox is thought to be aiming for 2 million subscribers within the first two years. “That is very ambitious,” said Digital TV Research principal analyst Simon Murray. “People are now more used to SVOD, but 2 million still looks optimistic.”

The BritBox venture is complicated by the fact that the BBC and ITV already have free online catchup services, the iPlayer and ITV Hub, both of which will continue to exist. BBC’s iPlayer is in the throes of getting permission to extend its window from 30 days to a year. If that happens, then viewers would have the chance to see most BBC content on linear and then on demand for a full 12 months on the iPlayer before it lands on BritBox. Shows will move from ITV Hub to BritBox after 30 days.

BritBox is banking on its huge catalog of titles as its selling point, including BBC and ITV classics not available on the iPlayer and ITV Hub, plus new originals only available on BritBox. But the “tens of millions” of pounds that BritBox says it is allocating for original content pales next to the billions being shelled out by Amazon, Apple and Netflix, whose local ambitions were underscored with its deal to turn historic Shepperton Studios, outside London, into its British production hub.

As a buyer, BritBox must also stump up the money for rights to BBC and ITV shows that were made by third parties. It has already done deals with Endemol Shine Intl. for “Broadchurch” and NBCUniversal for “Downton Abbey,” both of which aired on ITV.

BBC series currently playing on Netflix in the U.K. include “Doctor Who,” “Sherlock,” “Luther,” “Call the Midwife,” “Top of the Lake,” and “Peaky Blinders,” as well as blue-chip natural history franchises “Blue Planet” and “Planet Earth.” But the BBC only controls some of these, meaning that BritBox will need to pay outside distributors for the rest.

Shows that ITV broadcasts and controls the rights to include comedy series “Benidorm” and reality hit “Love Island.” But BritBox would need to license “Marcella,” which aired on ITV but is distributed by Cineflix Rights.

Both the BBC and ITV will pull their programming from other streamers in the U.K., just as Warner is pulling “Friends” from Netflix in the U.S. But perhaps mindful of not ruffling the feathers of the U.S. streamers – who will remain deep-pocketed co-production partners and big buyers of finished shows for other territories – the BBC has declined to say exactly when “The Office,” “Gavin and Stacey” and other shows will move over to BritBox.

Whether other British broadcasters join the BritBox party remains to be seen. Talks are ongoing with Viacom’s Channel 5 and pubcaster Channel 4, but both those channels are beefing up their own on-demands services by adding shows from third parties to box sets of their own series. Channel 5 has added more than 1,000 of hours to My5 from third parties including A+E and PBS. Channel 4 has licensed almost 1,000 hours from Vice for its revamped free All4 service and has tried out a pay version.

“It’s not going to steal Netflix’s crown, but I’d be relatively bullish about its chances as part of, rather than the core of, a wider in-home streaming bundle,” Guy Bisson, Ampere Analysis’ research director, said of BritBox’s prospects. “Of course, it comes down to execution, but the key is the exclusive content they are planning. If that’s of high enough volume, quality and frequency, then I definitely think it has a solid chance in the U.K.”