The fastener 2 comprises interlocking first 20 and second 21 portions, the first portion is deformable by the relative movement of the second away from the first and requires a sufficient pulling force to uncouple. The first portion may resume its shape once these portions are uncoupled. The first and second portions may form male 20 and female 21 portions respectively, the male portion 20 may comprise at least one arm 26 and shoulder 23. The male portion may comprise arms that are coupled by a resilient member 27 such as a compression spring. While the female portion 21 may comprise at least one arm 28 and elbow 25 which may form an aperture 24 to receive the male portion. The releasable fastener may in particular be used as part of a surcingle buckle for fastening around a horses girth.
