Originally Posted by
South London Bon Viveur
I have been pulled for a few secondary searches and apparently the culprit was a small but quite thick/fat book (not dissimilar to a pack of playing cards in shape and size) which then had to be swabbed. I have removed the little fat book (without reading it) and things seem to be plain sailing again.
Stacks in the form of books, or more usually stacks of credit cards, can cause problems if the algorithm doesn't reconcile the item to a book. At a certain point the density becomes too big and needs manual inspection. If you travel regularly with a particular item then you will probably work out tactics around that.
Playing cards are different. They are usually 2 cards, bonded with something like polyvinyl acetate and coated with nitrocellulose. If you were around in the 1980s then these compounds may seem familiar, guncotton for those ex-Forces. Sufficient for the Birmingham Six to end up in prison for something they didn't do. So while playing cards are sold airside in many airports including LHR, It's probably best to get any new pack of playing cards well used before travel, and scanned separately.