Higson and Hesmondhalgh join Broadchurch for finale

Charlie Higson and Julie Hesmondhalgh will join the cast for a storyline that focuses on an investigation into a serious sexual assault

Actor and writer Charlie Higson and former Coronation Street actress Julie Hesmondhalgh are joining the third and final series of Broadchurch.

They will appear with the ITV police drama's stars David Tennant and Olivia Colman for a story about a serious sexual assault.

Scriptwriter Chris Chibnall said it will mark the show's "final chapter".

"We have one last story to tell featuring familiar faces and new characters," he said.

"I hope it's a compelling and emotional farewell to a world and show that means so much to me."

After Broadchurch ends, Chibnall will be moving to replace Steven Moffat as the head writer and executive producer for BBC One's Doctor Who.

ITV has not yet revealed who Hesmondhalgh and Higson will play but filming will begin this summer on the eight-part police drama series in Dorset.

Other new members of the cast will include Mistresses star Sarah Parish and Murdered by My Boyfriend Bafta-winner Georgina Campbell.

Higson, who wrote and appeared in the hugely successful comedy sketch series The Fast Show, has also featured in the ITV drama Jekyll and Hyde, which failed to hit the mark with critics or viewers.

Olivia Coleman and David Tennant's detective characters will draw the hit show to its conclusion

But, said Higson on Twitter, the lack of a second series of that show has allowed him to take on Broadchurch.

"The one good thing to come out of ITV not making another Jekyll and Hyde is that I have time to do other things, like acting in Broadchurch," he said.

"Really looking forward to joining the team."

Hesmondhalgh is best known for formerly playing transgender character Hayley Cropper on long-running soap Coronation Street. She left the series in 2014 after a tear-jerker storyline, which saw Hayley die of cancer.

Series stalwarts Jodie Whittaker and Andrew Buchan will return as Beth and Mark Latimer. Arthur Darvill will again be playing local vicar Paul Coates and Carolyn Pickles will reprise her role as newspaper editor Maggie Radcliffe, along with Adam Wilson as Ellie's son Tom.

Broadchurch had audiences gripped when it launched in April 2013, with a peak audience of 8.9 million viewers.

The drama about the death of an 11-year-old boy also won critical acclaim, along with Bafta and RTS awards.

A second series was shown in January 2015, with the first episode pulling in a healthy eight million viewers but a US version of the series, starring David Tennant, was cancelled after its first series.