Viewers may have to wait until spring 2019 for the next series of Line of Duty

According to senior production sources it will be quite a wait for series five, possibly up to two years.

Writer Jed Mercurio (below) has his hands full with The Bodyguard – his new six-part BBC1 series set in the Met Police’s Royalty and Specialist Protection Branch (RaSP) – so it looks like Line of Duty fans will have to wait.

Mercurio recently told RadioTimes.com that he was only half way through writing The Bodyguard and was “a long way from casting”. Production on the new drama is not expected to take place before the autumn, say BBC sources.

This means that Line of Duty series five is expected to be written next year and filmed in the autumn of 2018 for a possible broadcast as late as spring 2019.

This would not be the first time that fans were obliged to wait for their next fix of the brilliant drama.

There was a 20-month gap between series one and two. Series one premiered in June 2012 followed by series two in February 2014. Series three aired in March 2016 followed by series four which began in March this year.

Speaking to RadioTimes.com earlier this year, Mercurio laid out his plans for the long-term future of the show.

“If, by the time we get to the development of series five, there are no further series commissioned, then we have to approach series five as if it’s the last,” he said. “If we know we have got a sixth series then we are able to look ahead.

“I have got an idea of how things will conclude or, more accurately, the kind of story we need to get into for that to be dramatised," he added. "Whereas if I know series five is not the last series then I have other ideas that are more standalone in terms of what the story is.”

Asked whether he had an idea for a final series in his head, he said: “Yes, the conclusion, yes. They are half ideas. I haven’t fully developed them. What will happen over the course of this year is that we will know whether we are doing more than just series five and everything will follow on from that.”

How many series would he like to make if the decision was his? “I certainly would make six. Whether I would go beyond six would depend on how series five went.

“One of the advantages of commissioning two ahead is that it allows you to take a breath and look forward to the next one, and at the moment there is a great appetite among all of us involved in the programme to do more. What we don’t know is whether there will come a point where we kind of lose that enthusiasm to keep going back."

A BBC spokeswoman said that it was “too early to say” what the plans were but Corporation sources have not explicitly denied suggestions that a fifth series will have a longer wait.

But if there is a long gap then maybe Adrian Dunbar’s fab Ted Hastings could use his charm and clout to hurry things up...