Lord Fellowes, speaking at the launch of his new musical The Wind in the Willows, told the Evening Standard: “I’ve done some work on it because I don’t want want to be caught out if [the producers] suddenly say yes and then it’s all go.”

But the 67-year-old admitted there were still a lot of uncertainties. “Can we round up all the cast? Can we get them?” he questioned. “Also we just need the green light at the beginning. So I don’t know anymore than that at the moment to be honest.”

No other details - including information about a possible plot or when the film would be set - were revealed in the interview.