With the U.K. government set to introduce in April what’s likely to be a generous tax incentive for big-budget TV productions, it appears that the sector, given a shot in the arm by the success of “Downton Abbey,” might be on the verge of a true breakout — and Hollywood is taking notice.

While “Downton,” produced by NBC-Universal’s London shingle Carnival and shot in the U.K., is the exception rather than the rule — most high-budget TV shows produced by U.K.-based companies are not lensed in Blighty — with tax credits on the horizon, that is set to change. Many see a future that offers heightened worldwide marketability for U.K.-produced fare and increased collaboration with the U.S., underscored by speculation recently that Sony Pictures Television is interested in buying Blighty’s Left Bank Pictures.

The tax incentive plan is hazy, with details still being formulated, but a U.K. production biz lobby group, the TV Coalition, is pressing for the incentive to be based on the nation’s film tax credit. If its proposals are adopted, the incentive would be worth 20% of the U.K. spend, with a requirement for a minimum budget level of £1 million ($1.6 million) for an hourlong.

As well as persuading productions to stay home, the incentive could also lure more U.S. network shows to Blighty. At present, even skeins that could be considered culturally British are shot elsewhere. For example, Showtime’s “The Tudors” and Starz’s “Camelot” used locations in Ireland.

For most U.K. producers, shooting locally is too expensive when there are countries nearby that offer production tax incentives.

“Parade’s End,” Tom Stoppard’s adaptation of the Ford Madox Ford novels, shot 43% of its scenes and undertook more than 80% of its post-production in Belgium. U.K. production house Mammoth, which produced the series for HBO, the BBC and its international sales arm BBC Worldwide, says that if a tax incentive had been in place, the lion’s share of the filming and almost all the post-production would have taken place in the U.K.

Even countries some distance away attract Blighty TV productions. Action series “Strike Back,” which Left Bank produces for Cinemax/HBO in the U.S. and satcaster BSkyB in the U.K., is shot almost entirely in Hungary and South Africa.

According to a recent report by Stephen Bristow, associate director at media consultancy RSM Tenon, and Charles Moore, a partner at law firm Wiggin, a 20% tax incentive is likely to bring more than $545 million in additional production spending per year to the U.K.

High-end TV drama is very mobile in terms of location, and the existence of a tax credit is central to a country’s appeal, the report states. “HBO, for example, said that 10 years ago, 10% of their production spend was shot in locations where incentives were offered. Today, this figure has increased to 85% of their total production spend,” the report notes.

Armed with a tax incentive, the U.K. could become a rival even to Canada in vying for U.S. network shows, says Andy Harries, chief executive of Left Bank, which produces Kenneth Branagh-starring crime series “Wallander” for WGBH Boston and the BBC, as well as features, such as “The Queen.”

“(The U.S. networks) will be looking to the U.K. in the same way that they look to Canada: If it is cheaper to (film) in the U.K. and they can deliver a product that works in their domestic market, they will(come),” Harries says.

Maria Kyriacou, managing director of ITV Studios Global Entertainment, the U.K. broadcaster’s international distribution arm, says U.S. cable networks already are far more willing to consider shows from international producers.

“There are lots of opportunities right now for co-productions and for them to buy shows,” Kyriacou says, adding that streaming outlets such as Netflix and Hulu have been having success with some of their high-end dramas.

Kyriacou says that incentives could mean more spending-power for U.K. production companies, enabling them to add well-known thesps or high-end special effects that improve the chances of sales in the international market.

“Recognizable talent helps people pay attention to the shows,” Kyriacou says. For example, the casting of Jeremy Piven as the lead in costume drama “Mr. Selfridge,” which ITV Studios Global Entertainment is distributing, is helping the show’s worldwide sales. In the U.S. “Mr. Selfridge” has been picked up by PBS’ “Masterpiece,” home to “Downton Abbey.”

According to Harries, incentives might lead to a growing number of shows that combine the best of U.S. and U.K. creative talent. “What probably one would try to achieve is some kind of hybrid that will have some American casting for sure, but somehow marries American and English content satisfactorily, (and will play in both countries),” he says. “The tax break will undoubtedly add energy and financial imperative.”

Harries points to comedy series “Episodes,” produced by the U.K.’s Hat Trick Prods. for the BBC and Showtime Networks, as an indication of the way the biz may develop. Set in Los Angeles, the show stars Matt LeBlanc, and is penned by Hollywood scribes David Crane (“Friends”) and Jeffery Klarik (“Mad About You”), but is shot almost entirely in the U.K. Production for the second season included a six-day shoot in Los Angeles for exteriors, but the rest of the show was shot at London studios, and at locations around the city that doubled for Los Angeles.

Hat Trick wouldn’t reveal the budget, but Harries says he was told it was about half to two-thirds of what it would have been if it had been shot in the States.

And with incentives, that number would be friendlier still.