Suranne Jones told the Radio Times that new episodes of the ITV1 drama will begin filming in November.
"[Series co-creator] Sally Wainwright is such an amazing writer and has so many amazing ideas," said her co-star Lesley Sharp.
"She gives you some sort of clue about what might happen and then you open the script and none of it's there and it's something even better."
The crime drama - which began in May 2011 - follows the personal and professional lives of DC Rachel Bailey (Jones) and DC Janet Scott (Sharp) of the fictional Manchester Metropolitan Police.
The Scott & Bailey series two finale pulled in 6.44m viewers for ITV1.
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Watch a trailer for Scott & Bailey below: