Police drama The Bill is preparing for its first live episode on Thursday as it celebrates its 20th anniversary.
Long-serving star Trudie Godwin with co-star Todd Carty
A 200-strong crew will guide cast members through the hour-long episode at the programme's south London base.
The Bill first appeared on ITV in 1983 as a one-off drama called Woodentop, with its debut series beginning the following year.
"Live drama rarely happens on screen these days. It's nerve-wracking for everyone," a show spokesman said.
Stars who have appeared in The Bill over the years include former Spice Girl Emma Bunton, Full Monty star Robert Carlyle and Nil By Mouth actress Kathy Burke.
Actor Mark Wingett - who played probationary officer Jimmy Carver in Woodentop - still appears in The Bill today, as does Trudie Godwin (June Ackland). Both will appear in the live programme.
The Bill started life as a series of hourly episodes, based at the fictional Sun Hill station in east London, but from 1988 it was transmitted in half-hourly episodes, twice each week, all year round.
Despite production company Thames losing its ITV franchise, the network stuck with the series and commissioned a third weekly instalment in 1993.
It reverted to its old hour-long format in 1998, and its storylines now focus on the private lives of the officers at Sun Hill.
It now attracts about eight million viewers each week.
The live episode goes out at 2000 GMT on Thursday.