Genghis,
....Christmas crackers. Provided the Christmas crackers are in their original retail packaging, they may be carried by passengers. Check with your airline as some airlines have decided not to allow the carriage of crackers......
The above is a clip from the document 'What Can I Carry?' which is on the CAA's website as srg_dgo_whatcanIcarry20090925.pdf
I got it from my recent visit to Global Air Training who have a pretty good Dodgy Goods team but can not seem to attach the document to this post. PM me if you would like a copy by email
You will find a link to it here
Information for Passengers | Flight Operations | Safety Regulation
Note, it does say that it is operator specific. Updated on 24 Sept 2009 so fairly recent. It's under Miscellaneous Items - scroll down.
Regards
MM