When Eastenders had pulling power that casting was all deliberate to pull in fans to watch.
I do wonder if we are seeing the slow death of long running shows. I have not watched Holby for a decade now. I think the last time I saw it Patsy Kensit was in it.
Patsy Kensit returned once, in 2019.
Marc Elliott, who played Syed Masood in EastEnders played the abusive Isaac in Holby City and he returned that year too.
They did cast some familiar names/familiar faces from other shows. Angela Griffin and Tina Hobley had been in Coronation Street. Belinda Owusu was Libby Fox on EastEnders before she did Holby City. Kaye Wragg had been in The Bill. Art Malik played Zubin. Robert Powell and Sharon Maughan were regulars. Robert Powell got to be CEO.
Bryan Murray played surgeon James Roberts in some Casualty episodes, beginning with the Casualty episode that first introduced Michael French as Nick Jordan, in preparation for the beginning of Holby City. Then Bryan Murray appeared as Roberts in more Casualty episodes and the same character in early episodes of Holby City. Paul Shane was in it for a while. And then came back for a one-off and his character died. Jeremy Edwards had been an original cast member on Hollyoaks, then returned to Hollyoaks last year, alive and well, two decades after his character had died in a jet-ski accident. Patsy Kensit’s character’s mother was played by Deborah Grant and her in-laws were played by Ronald Pickup and Jane Asher. Susannah York was in several episodes in two series as trust executive executive Helen Grant and also did a couple of episodes of Casualty. Leslie Phillips appeared as Tom Campbell-Gore’s father. Ade Edmondson was in a few series as Abra Durant. Patricia Potter had been in Brookside and she reappeared in Holby City in 2019, despite her character having been dead for 13 years. Martin Hancock, who had played Spider Nugent in Coronation Street, did some episodes. John Michie was well known from Taggart and Coronation Street, before joining Holby City as neurosurgeon and former CEO, Guy Self, and has made several crossover appearances on Casualty. Stella Gonet played CEO too (and guested in Casualty).
Judy Loe (who was in Ace of Wands!) played CEO Jan Goddard on Casualty. Jan quickly got into and a sexual relationship with Charlie Fairhead and promoted him, until Charlie dumped her, after she backstabbed and sacrificed his friend and colleague to the press and replaced him with Simon MacCorkindale. After which Jan never ever came downstairs again and stayed upstairs on Holby City, where she slept with Tom Campbell-Gore (Denis Lawson… who returned for three episodes in 2019, one of which featured Lorraine Chase) and she promoted Tom, after which he dumped her.
Alex Walkinshaw had been in The Bill, before he joined Casualty. But he wanted to spend more time with his family. So he went upstairs to Holby City instead, which reunited him with Rosie Marcel, whose guest character on The Bill had slept with his character. So Holby City sneaked in a reference to it. Joseph Millson had been a regular on The Sarah Jane Adventures, including a prominent part in the episode (with Jane Asher) that got CBBC it’s highest ever ratings.
And Casualty’s Maxwell Caulfield (that name rings a bell) popped over to Holby City and immediately died a horrible death there.
Phyllis Logan, Jemma Redgrave, Paul McGann were in it. Current cast includes Jo Martin and Debra Stephenson.
And both incarnations of Connie Beauchamp’s father, actors Donald Sumpter and Ken Bones, appeared together as Time Lords in Doctor Who.