Customers buying a bunch of flowers who try to add a free message containing them are prevented from completing their order.
An on-screen notification, which pops up if any blocked words are entered, reads: 'Sorry, there's something in your message we can't write.'
'Christ' and 'Jesus Christ' join other banned words including 'f***' and 'gay' - but some terms including jihad, Buddha and Allah are accepted.
'Terrorist' and 'd**k' can also be included in messages.
The policy emerged earlier today after one customer was stopped from buying a £35 bouquet for a funeral because she said in the gift message that it was from a family in 'Christ Church Teddington'.