Customers ordering flowers online from Marks & Spencer can use words such as "jihad", Buddha and Allah inmessages.
But other words such as "Christ" and "Jesus Christ" are banned, along with profanities, and the word "gay".
Customers who try to add a free message when they buy flowers cannot complete their order if they attempt to use one of the banned words. A pop-up message tells them: "Sorry, there's something in your message we can't write."
The restrictions were exposed by The Sunday Times after a customer was prevented from buying a £35 bouquet for a funeral. Clergy wife Geraldine Stockford tried to attach a message to the flowers stating that they were from a family in "Christ Church Teddington". She was prevented from doing so and when she telephoned customer services to find out why, was told it must be a blocked word. The customer services operator did then agree to write the message for her as she wished it.
The full message read: "Thank you for your care and practical help for Margaret in her last days . . . With love from her church family, Christ Church Teddington." The late Margaret, 93, whose funeral is this week, was a church member for 87 years.
The former Archbishop of Canterbury, Lord Carey of Clifton, said: "If Christ becomes an offensive word in a Christian land then all of us should be alarmed."
A spokesman for Marks & Spencer said: "An automatic phrase checker is in place to prevent the use and misuse of certain words and it includes hundreds of words of varying nature. The words Jesus and Christ are included to prevent their misuse."
The Sunday Times reported that other religious terms, such as Allah, Mohammad and Buddha as well as hajj and jihad were permitted, but inputting swear words triggered the same message as Christ. The term "gay" was also blocked.
Andrea Minichiello Williams, chief executive of Christian Concern, said: "It is a sad state of affairs if the start point is to assume the word Christ is being used to be offensive."