A method for detecting a first allele of a single nucleotide polymorphism in a nucleic acid sequence, wherein the method comprises (a) amplifying under isothermal conditions and stringent conditions a nucleic acid sequence from a sample, in a reaction mixture comprising (i) the nucleic acid sequence, (ii) a nucleic acid polymerase, (iii) a nucleoside triphosphate mixture, (iv) a forward inner primer targeting the first allele (FIPa1), comprising a F1c region which anneals to a F1 region of the nucleic acid sequence in the presence of the first allele and a F2 region which anneals to a F2c region of the nucleic acid sequence, (v) a backward inner primer targeting the first allele (BIPa1), comprising a B1c region which anneals to a B1 region of the nucleic acid sequence in the presence of the first allele and a B2 region which anneals to a B2c region of the nucleic acid sequence, (vi) a forward blocking primer targeting a second allele of the SNP, comprising a B1c region which anneals to the B1 region of the nucleic acid sequence in the presence of the second allele, and (vii) a backward blocking primer targeting the second allele, comprising a F1c region which anneals to the F1 region of the nucleic acid sequence in the presence of the second allele, wherein the F1 region of the nucleic acid sequence and the B1 region of the nucleic acid sequence both contain the SNP, wherein BBa2 may prime extension from its 3' end and/or FBa2 may prime extension from its 3' end, and (b) detecting an amplified nucleic acid sequence, wherein the detection of an amplified nucleic acid sequence indicates the presence the first allele of the SNP; wherein, in the presence of the first allele, the annealing of the F1c region of FIPa1 and the B1c region of BIPa1 to the nucleic acid sequence is more energetically favourable than the annealing of FBa2 and BBa2 to the nucleic acid sequence. (a) amplifying under isothermal conditions and stringent conditions a nucleic acid sequence from a sample, in a reaction mixture comprising (i) the nucleic acid sequence, (ii) a nucleic acid polymerase, (iii) a nucleoside triphosphate mixture, (iv) a forward inner primer targeting the first allele (FIPa1), comprising a F1c region which anneals to a F1 region of the nucleic acid sequence in the presence of the first allele and a F2 region which anneals to a F2c region of the nucleic acid sequence, (v) a backward inner primer targeting the first allele (BIPa1), comprising a B1c region which anneals to a B1 region of the nucleic acid sequence in the presence of the first allele and a B2 region which anneals to a B2c region of the nucleic acid sequence, (vi) a forward blocking primer targeting a second allele of the SNP, comprising a B1c region which anneals to the B1 region of the nucleic acid sequence in the presence of the second allele, and (vii) a backward blocking primer targeting the second allele, comprising a F1c region which anneals to the F1 region of the nucleic acid sequence in the presence of the second allele, wherein the F1 region of the nucleic acid sequence and the B1 region of the nucleic acid sequence both contain the SNP, wherein BBa2 may prime extension from its 3' end and/or FBa2 may prime extension from its 3' end, and (i) the nucleic acid sequence, (ii) a nucleic acid polymerase, (iii) a nucleoside triphosphate mixture, (iv) a forward inner primer targeting the first allele (FIPa1), comprising a F1c region which anneals to a F1 region of the nucleic acid sequence in the presence of the first allele and a F2 region which anneals to a F2c region of the nucleic acid sequence, (v) a backward inner primer targeting the first allele (BIPa1), comprising a B1c region which anneals to a B1 region of the nucleic acid sequence in the presence of the first allele and a B2 region which anneals to a B2c region of the nucleic acid sequence, (vi) a forward blocking primer targeting a second allele of the SNP, comprising a B1c region which anneals to the B1 region of the nucleic acid sequence in the presence of the second allele, and (vii) a backward blocking primer targeting the second allele, comprising a F1c region which anneals to the F1 region of the nucleic acid sequence in the presence of the second allele, wherein the F1 region of the nucleic acid sequence and the B1 region of the nucleic acid sequence both contain the SNP, wherein BBa2 may prime extension from its 3' end and/or FBa2 may prime extension from its 3' end, and (b) detecting an amplified nucleic acid sequence, wherein the detection of an amplified nucleic acid sequence indicates the presence the first allele of the SNP; wherein, in the presence of the first allele, the annealing of the F1c region of FIPa1 and the B1c region of BIPa1 to the nucleic acid sequence is more energetically favourable than the annealing of FBa2 and BBa2 to the nucleic acid sequence.