Theresa May has become embroiled in a row over an Easter egg hunt, saying a decision not to mention the religious festival in the title is "absolutely ridiculous".
Chocolate giant Cadbury and the National Trust are running a spring event at around 300 of the conservation charity's properties called the Cadbury Egg Hunt.
The word Easter is mentioned several times on the National Trust webpage promoting the hunts, but does not feature in the event logo.
The prime minister has joined the Archbishop of York in condemning the move.
Mrs May, who is a vicar's daughter and a member of the National Trust, told ITV News: "I think the stance they've taken is absolutely ridiculous and I don't know what they're thinking about.
"Easter's very important. It's important to me, it's a very important festival for the Christian faith for millions across the world.
"So I think what the National Trust is doing is frankly just ridiculous."
On Tuesday morning, the National Trust added the word "Easter" to the banner at the top of its webpage promoting the hunt. It now reads: "Join the Cadbury Egg Hunts this Easter."
A National Trust spokeswoman said it had been added to provide "further clarification" that the religious festival is a central part of the events.
The word is now mentioned five times on the page promoting the hunts.
Cadbury was founded by Quaker John Cadbury in 1824 and Dr John Sentamu, the Archbishop of York, told the Daily Telegraph: "To drop Easter from Cadbury's Easter Egg Hunt in my book is tantamount to spitting on the grave of Cadbury."
The National Trust said suggestions it was downplaying the significance of Easter were "nonsense", while Cadbury dismissed the archbishop's claim as "simply not true".
Dr Sentamu said: "If people visited Birmingham today in the Cadbury World they will discover how Cadbury's Christian faith influenced his industrial output.
"He built houses for all his workers, he built a church, he made provision for schools.
"It is obvious that for him Jesus and justice were two sides of the one coin."
The National Trust website invites people to "Join the Cadbury Egg Hunts" before adding: "Join us over the Easter holidays to run through muddy woodlands, around mystical lakes and along nature trails on a Cadbury Egg Hunt."
A National Trust spokesman said: "It's nonsense to suggest the National Trust is downplaying the significance of Easter. Nothing could be further from the truth.
"We host a huge programme of events, activities and walks to bring families together to celebrate this very special time of year.
"A casual glance at our website will see dozens of references to Easter throughout.
"Our Easter events include our partnership with Cadbury's, which has been running Easter egg hunts with us for 10 years.
"They've proved consistently popular with our members and visitors. As part of its wider marketing activity at Easter, Cadbury's will always lead on the branding and wording for its campaigns."
A Cadbury spokeswoman added: "It is simply not true to claim that we have removed the word 'Easter' from our marketing and communication materials.
"Each year our Easter campaigns have a different name and this year our seasonal campaign is called the Cadbury's Great British Egg Hunt.
"It is clear to see that within our communications and marketing we clearly state the word Easter and include it in a number of promotional materials, including our website, where we do also promote our partnership with National Trust at this seasonal time of year."