Doon Mackichan, who plays Cathy in hit sitcom Two Doors Down, is leaving the show.

However, Siobhan Redmond will be joining the cast for the next series. The actor's sitcom CV includes The High Life and The Smoking Room.

As revealed by British Comedy Guide in July, the BBC Two comedy is set to return for a sixth series and Christmas special later this year.

The BBC has now confirmed this news, saying: "Two Doors Down, the hugely popular Scottish sitcom, set in the fictional suburban street of Latimer Crescent, will be returning to BBC Two and BBC iPlayer later this year with brand new episodes and a Christmas special, which sees the neighbours test their friendships to the limit.

"Bursting with comic vitality, acid-tongued put downs and ultimate awkwardness these very funny, frequently exasperating, new episodes bring us back in to the world of these memorable characters who we, probably, wouldn't want to have living next door."

Talking about the plot, they explain: "Beth (Arabella Weir) and Eric's (Alex Norton) peaceful suburban existence is continually punctured by the inappropriate behaviour of their fellow residents, who are often rude about their hospitality and frequently outstay their welcome. Lifelong hypochondriac Christine (Elaine C Smith) never misses an opportunity to sponge a cuppa off Beth while undermining her at the same time; Colin (Jonathan Watson) needs his neighbours more than ever this series as his wife Cathy has left him and now lives abroad, but he can't help oversharing personal details; and ever-positive Michelle (Joy McAvoy) continues to struggle with hapless Alan's (Graeme Stevely) imperfections. It seems Beth and Eric's only support comes in the form of loving son Ian (Jamie Quinn) and his wide-eyed fiancé Gordon (Kieran Hodgson)."

The reason for Doon Mackichan's departure has not been given. The BBC did say: "It has been absolutely fantastic to have Doon in the show. She'll always be part of the Two Doors Down family and we wish her all the best. Her character Cathy has been a great source of horror, entertainment and laughs for millions of viewers over the years. We await news of what will become of poor Colin. What will he do with all the empties? And who'll microwave his dinner for him?"

Details on the character Siobhan Redmond will play will be revealed closer to the series being broadcast.

Talking about the new episodes, Steven Canny, executive producer for BBC Studios, says: "It's such a pleasure and privilege to be back making Two Doors Down. It's a phenomenal crew, a brilliantly funny cast and the beautifully crafted scripts are a constant source of surprise and delight sprinkled with cruelty. I'm really looking forward to the audience seeing the new ways we've found to torment poor Beth and Eric."

Commissioning editor Seb Barwell adds: "We're delighted to bring six series up for Two Doors Down, a show that continues to delight audiences with its miniature masterpieces of contained comedy."