Thirty-five years ago, one of the biggest events in UK TV occurred when BBC One revealed the identity of JR’s assassin in Dallas. A massive 22 million viewers watched the episode on 21 November 1980.

In those faraway days, big American series such as Starsky and Hutch were popular constituents of the BBC One schedule.

In the 1990s, hit comedies Friends and Frasier helped define Channel 4. Today, BBC One has no acquired series, while ITV only periodically re-enters the genre – and with scant success. Meanwhile, Channel 4’s acquired comedy tradition has given way to drama.

It’s not that there are fewer imports – indeed, there have probably never been so many. Rather, it is where we find them: now, they tend to play out on the smaller digital networks.

Imports are cost-effective for networks with smaller budgets: each episode will be transmitted numerous times. And for those channels that can afford exclusive rights to the latest, talked-about property, series such as Sky Atlantic’s Game of Thrones can help boost subscriptions.

Free-to-air ITV2 saw an opportunity to bolster audience share (and thus ad revenue) with the purchase of hit US animation Family Guy, which has performed so well for BBC Three.

One downside to acquired programming is, of course, a lack of control. The fate of a series is decided by its success or failure on its home US network. A loyal following in the UK for the first season is no guarantee that a US-made drama will reach its denouement: Channel 5 viewers were left hanging in 2010 when FlashForward was cancelled after one series by ABC – with critical plot developments still unresolved.

The last time ITV1 dipped its toe in the market for imported shows was with two series of The Americans, from US cable network FX.

When ITV launched the second series (at 9:20pm on Saturday, 15 March 2014), Broadcast noted that it had scraped together an audience of just 1.3 million (a 7% share): nowhere near enough for primetime on ITV’s flagship channel.

Given this lack of success on the main channel, the third series was moved this summer to pay-channel ITV Encore.

Channel 4’s fifth series of Homeland (from US cable network Showtime) has just finished its 12-episode, Sunday-­night run, as has the channel’s 10-episode second season of Fargo. More family-friendly series include ABC’s Marvel’s Agents of SHIELD. The show played at 8:00pm on Fridays from autumn 2014 on Channel 4. 

BBC Two’s only acquired series last year was Odyssey, starring British actor Anna Friel. It aired in the summer after its spring debut on NBC.

Of Britain’s PSB networks, Channel 5 remains the most acquisitions heavy: last year it played Gotham, The Mentalist, NCIS: New Orleans and Under the Dome, as well as the Australian series Wentworth Prison, among others.

Channel 5 made great use of the CBS drama franchise CSI to establish its presence and personality. Gradually, the many CSI variants have been cancelled in the US.

The main UK networks’ digital offspring make more use of acquired programming than the parent channels. CBS sitcom The Big Bang Theory has been hugely successful for Channel 4’s youth channel, E4: in its premiere transmission slot (Thursday at 8:30pm) the show can even outdo Channel 4.

To maximise its value, E4 uses the many Big Bang Theory episodes available to populate its schedule. In the week beginning 26 October, for example, the channel transmitted 55 episodes across daytime, peak and late night.

E4 also found success with the ­science-fiction dramas The 100 and The Tomorrow People, both from The CW network. Despite achieving E4’s highest launch audience for a US series (1.4 million, or a 6% share, on 8 January, according to Broadcast), The Tomorrow People was cancelled by CW after just one series.

ITV’s youth-skewing channel ITV2 has been much more reliant on home-grown commissions, such as Celebrity Juice and The Only Way Is Essex and the brand extension The Xtra Factor. The acquisition slate mostly comprises films.

In March, however, ITV2 secured the rights to the latest series of US Fox network’s Family Guy. Arguably, this signalled a change of strategy for the channel, as the deal also included American Dad!, The Cleveland Show and Bordertown.

In pay-TV, the network’s primary aim, of course, is to grow subscriptions; US acquisitions are now playing a greater part in meeting that objective.

For example, Sky announced this spring that it would stop commissioning original shows for its female-oriented channel Sky Living: henceforth, the schedule would rely on acquisitions.

Since the channel relaunched in September 2013, only about 10% of Sky Living’s top 250 shows had been original commissions, according to Broadcast. One of the few was The Face, fronted by Naomi Campbell, which averaged 217,000 viewers (a 0.8% share) – well behind the slot average of  488,000 viewers and a 1.8% share. Acquired shows such as The Blacklist, Elementary and Criminal Minds regularly attract 1 million-plus audiences.

Stuart Murphy, then Director of Sky Entertainment Channels, explained at the time that this shift would mean a dramatic increase in investment in home-grown shows for Sky 1.

It is interesting that Lucky Man, a new 10-part original series commissioned by Sky 1 for this year, is the brainchild of Marvel comics creator Stan Lee. Perhaps it is an attempt to sprinkle some of the acquired magic over UK-­made content.

In the week beginning 26 October, E4 transmitted 55 episodes of The Big Bang Theory

In the meantime, the heart of Sky 1’s evening schedule has moved away from original commissions. Back in the autumn of 2013, Sky 1’s weekday schedule at 8:00pm was a mix of original programming and acquired. Originals included the documentary series All Aboard: East Coast Trains and Inside RAF Brize Norton. Imports included Fox Network’s Glee, superhero series Arrow from The CW and ABC sitcom Modern Family.

By autumn 2015, the landscape of Sky 1 at 8:00pm was very different, with US shows on four nights a week: ABC’s The Muppets and Modern Family on Monday, CW’s The Flash on Tuesday, Arrow on Wednesday and CBS’s Supergirl on Thursday.

The move has helped Sky 1’s performance in the slot. For example, on 21 November 2013, Inside RAF Brize Norton achieved 462,000 viewers (including time-shifting), while Supergirl on 5 November 2015 achieved 1.3 million (also including time-shifting).

Sky Atlantic has an output deal with US cable network HBO. Unsurprisingly, the channel offers a diet of predominantly American programmes with some home-grown shows, such as Fortitude and The Last Panthers. 

On 13 April 2015, HBO’s fantasy epic Game of Thrones drew an audience of 1.6 million (a 7% share) in the overnight ratings, the best performance ever for Sky Atlantic. In the process, it beat BBC Two, Channel 4 and Channel 5. The consolidated audience was 2.6 million.

Talked-about programmes such as this help to put a channel on the map but do not always translate into ratings successes. Mad Men, for example, was never watched by more than 500,000 viewers in the UK, even when it was on the more widely available BBC Four.

But the show was a key part of Sky Atlantic’s original marketing campaign: it helped get the channel noticed and set the tone for classy content.

With a further commitment to not just buy, but to co-produce, original dramas with HBO, Sky is expanding on the traditional acquisition deal. The network finds itself competing in a race to own as many rights as possible as the international programme sales market heats up, especially in drama – the value of a good script has never been higher.

The UK incarnation of US channel Fox has recently scored a significant success with The Walking Dead from the US cable network AMC. It has rated extremely well: the episode on Monday 2 November achieved an audience of 1.8 million, including time-shifting – more than Sky 1’s Supergirl that week.

The Walking Dead repeats proliferated through the schedule: in the week commencing 26 October, the third episode of the sixth series was shown eight times in all.

In August, BT launched the US cable channel AMC exclusively to its UK customers. Its best show is Fear the Walking Dead, which attracted 254,000 viewers on 31 August, including time-shifting.

It would be surprising if BT did not want to add The Walking Dead to its roster – so it is entirely possible that Fox’s lawyers in the UK are checking the fine print of its deal with AMC.

Gone are the days when we had to wait weeks or months for the latest US series to appear in UK schedules – largely because the fear of piracy has driven down the value of shows that are withheld for too long. Series typically launch soon after – and sometimes simultaneously with – the US premiere.

With its 300-plus channels all chasing content to drive subscriptions or advertising income, the UK’s appetite for the next big thing from across the pond is as voracious as it was back when Kristen shot JR.

But don’t expect to see these shows on the big free-to-air channels.