Anti-tampering devices for bottles

An anti-tampering bottle closure comprising an outer member in the form of a sleeve which is insertable into the neck of a bottle and an inner member in the form of a tubular valve body made of a substantially more rigid material than the sleeve. A ball valve is trapped within the valve body and adapted to allow liquid to be poured from the bottle when it is inverted but prevent liquid from being poured into the bottle when it is upright. The sleeve has a thickened wall portion and the valve body is axially insertable into the sleeve to compress the thickened wall portion against the neck of the bottle so as to resist radially inward deformation of the thickened wall portion of the sleeve and thereby lock the closure in the neck of a bottle. Preferably, the thickened wall portion of the sleeve forms an inwardly convex annular protrusion which is deformed outwardly into locking engagement with the bottle neck when the valve body is inserted into the sleeve.