A wood preservative formulation comprising a biocidal agent which is a copper or zinc ion complexed with an amino compound selected from the group consisting of ammonia, a water soluble amine or alkanolamine and an aminocarboxylic acid, and a cationic polymer selected from the group consisting of: (i) a compound of formula (ii) a compound of formula; and (iii) a compound of formula in which: n = 3 to 5000; n, = 0, 1 or 2; n 2 = 0 or 1; n 3 = 2 or 3 and when n = 3 the nitrogen atom carries a positive charge and a counter ion X - is present; R x groups, which can be identical or different, are hydrogen or a straight chain, branched or cyclic alkyl, alkenyl, alkynyl, alkanoxyl, aryl, -(C=O)H, -(C=O)R n, -CO 2 H -CO 2 R n, -CH 2 CO 2 H, -CH 2 CO 2 R n, CH 2 NR n R n, -(C=O)NR n R n, -CN, -(CH 2)n 4 -O-R n, in which; R n groups, which can be identical or different, are hydrogen or a straight chain, branched or cyclic alkyl, alkenyl, alkynyl, alkanoxyl or aryl; n 4 = 2 or 3; Ry is of the formula in which; R z = H or OH; a =0 to 10; b = 0 or 1; c = 0 to 10; d = 0 to 10; X - is any anion selected from chloride, bromide, iodide, fluoride, sulphate, phosphate, carboxylate especially propionate and lactate, carbonate, bicarbonate, nitrate, nitrite, hydroxide, cyanide; and * represents the bonds connecting the repeating units within the backbone of the polymer. (i) a compound of formula (ii) a compound of formula; and (iii) a compound of formula in which: n = 3 to 5000; n, = 0, 1 or 2; n 2 = 0 or 1; n 3 = 2 or 3 and when n = 3 the nitrogen atom carries a positive charge and a counter ion X - is present; R x groups, which can be identical or different, are hydrogen or a straight chain, branched or cyclic alkyl, alkenyl, alkynyl, alkanoxyl, aryl, -(C=O)H, -(C=O)R n, -CO 2 H -CO 2 R n, -CH 2 CO 2 H, -CH 2 CO 2 R n, CH 2 NR n R n, -(C=O)NR n R n, -CN, -(CH 2)n 4 -O-R n, in which; R n groups, which can be identical or different, are hydrogen or a straight chain, branched or cyclic alkyl, alkenyl, alkynyl, alkanoxyl or aryl; n 4 = 2 or 3; Ry is of the formula in which; R z = H or OH; a =0 to 10; b = 0 or 1; c = 0 to 10; d = 0 to 10; X - is any anion selected from chloride, bromide, iodide, fluoride, sulphate, phosphate, carboxylate especially propionate and lactate, carbonate, bicarbonate, nitrate, nitrite, hydroxide, cyanide; and * represents the bonds connecting the repeating units within the backbone of the polymer. n = 3 to 5000; n, = 0, 1 or 2; n 2 = 0 or 1; n 3 = 2 or 3 and when n = 3 the nitrogen atom carries a positive charge and a counter ion X - is present; R x groups, which can be identical or different, are hydrogen or a straight chain, branched or cyclic alkyl, alkenyl, alkynyl, alkanoxyl, aryl, -(C=O)H, -(C=O)R n, -CO 2 H -CO 2 R n, -CH 2 CO 2 H, -CH 2 CO 2 R n, CH 2 NR n R n, -(C=O)NR n R n, -CN, -(CH 2)n 4 -O-R n, in which; R n groups, which can be identical or different, are hydrogen or a straight chain, branched or cyclic alkyl, alkenyl, alkynyl, alkanoxyl or aryl; n 4 = 2 or 3; R z = H or OH; a =0 to 10; b = 0 or 1; c = 0 to 10; d = 0 to 10; X - is any anion selected from chloride, bromide, iodide, fluoride, sulphate, phosphate, carboxylate especially propionate and lactate, carbonate, bicarbonate, nitrate, nitrite, hydroxide, cyanide; and * represents the bonds connecting the repeating units within the backbone of the polymer.