The invention relates to a biocompatible, flexible, haemostatic sheet comprising: a cohesive fibrous carrier structure comprising a three-dimensional interconnected interstitial space; and distributed within the interstitial space, a plurality of reactive polymer particles comprising (i) a water-soluble electrophilic polymer carrying at least 3 reactive electrophilic groups that are capable of reacting with amine groups in tissue and blood under the formation of a covalent bond and (ii) a nucleophilic cross-linking agent that contains at least two reactive nucleophilic groups that are capable of reacting with the reactive electrophilic groups of the electrophilic polymer under the formation of a covalent bond, said reactive polymer particles having a diameter in the range of 0.5-100 μm and being present in an amount of at least 3% by weight of the fibrous carrier structure. When blood is absorbed by the haemostatic sheet of the present invention, the water-soluble electrophilic polymer in the reactive polymer particles starts dissolving as soon as these particles are ‘wetted’ by the blood, thereby allowing the electrophilic polymer to react with reactive nucleophilic groups in the blood and tissue, as well as with reactive nucleophilic groups of the nucleophilic cross-linking agent, thereby inducing blood coagulation and tissue sealing, both of which contribute to haemostasis.