A method for the detection of a primer extension product, the method comprising the steps of: a) providing one or more oligonucleotide primer groups, each group comprising one or more oligonucleotide primer sets, each set characterised by i) a first oligonucleotide primer having a target-specific portion and a 5' upstream fluorescence cassette-specific portion, and ii) a second oligonucleotide primer having a target specific portion wherein the oligonucleotide primers in a particular set are suitable respectively for hybridisation on complementary strands of a corresponding target nucleotide sequence to permit formation of a primer extension product, for example a PCR product and wherein the first oligonucleotide primer of each set in the same group contains a fluorescence cassette-specific portion that is capable of hybridising to the complement of the fluorescence cassette-specific portion of the first oligonucleotide primer of any set in the same group b) providing one or more cassette oligonucleotide sets, each set characterised by i) a first cassette oligonucleotide labelled with a fluorescent moiety that is a donor moiety and consists of a sequence that is capable of hybridisation to the complement of the fluorescence cassette-specific portion of the first oligonucleotide primer of any set in a given oligonucleotide primer group, and not comprising a target specific sequence portion; and ii) a second cassette oligonucleotide labelled with an acceptor moiety (for example a quencher moiety), wherein the second cassette oligonucleotide does not comprise target specific sequence and wherein the second cassette oligonucleotide is between 1 and 5 nucleotide bases shorter than the corresponding first cassette oligonucleotide; wherein each set of cassette oligonucleotides hybridises to one another to form a fluorescent quenched pair, wherein the fluorescent quenched pair has a Tm A, c) initiating the primer extension reaction thereby generating (if the relevant target polynucleotide is present) a complementary sequence to the relevant first oligonucleotide primer, such that the relevant second cassette oligonucleotide is less able to hybridise to the relevant first cassette oligonucleotide, whereby a signal is generated; and d) detecting the signal that is generated, wherein the primer extension reaction is performed at least in part at a Ta that is less than the Tm A or Tm As for the one or more fluorescent quenched pairs. a) providing one or more oligonucleotide primer groups, each group comprising one or more oligonucleotide primer sets, each set characterised by i) a first oligonucleotide primer having a target-specific portion and a 5' upstream fluorescence cassette-specific portion, and ii) a second oligonucleotide primer having a target specific portion wherein the oligonucleotide primers in a particular set are suitable respectively for hybridisation on complementary strands of a corresponding target nucleotide sequence to permit formation of a primer extension product, for example a PCR product and wherein the first oligonucleotide primer of each set in the same group contains a fluorescence cassette-specific portion that is capable of hybridising to the complement of the fluorescence cassette-specific portion of the first oligonucleotide primer of any set in the same group i) a first oligonucleotide primer having a target-specific portion and a 5' upstream fluorescence cassette-specific portion, and ii) a second oligonucleotide primer having a target specific portion b) providing one or more cassette oligonucleotide sets, each set characterised by i) a first cassette oligonucleotide labelled with a fluorescent moiety that is a donor moiety and consists of a sequence that is capable of hybridisation to the complement of the fluorescence cassette-specific portion of the first oligonucleotide primer of any set in a given oligonucleotide primer group, and not comprising a target specific sequence portion; and ii) a second cassette oligonucleotide labelled with an acceptor moiety (for example a quencher moiety), wherein the second cassette oligonucleotide does not comprise target specific sequence and wherein the second cassette oligonucleotide is between 1 and 5 nucleotide bases shorter than the corresponding first cassette oligonucleotide; wherein each set of cassette oligonucleotides hybridises to one another to form a fluorescent quenched pair, wherein the fluorescent quenched pair has a Tm A, i) a first cassette oligonucleotide labelled with a fluorescent moiety that is a donor moiety and consists of a sequence that is capable of hybridisation to the complement of the fluorescence cassette-specific portion of the first oligonucleotide primer of any set in a given oligonucleotide primer group, and not comprising a target specific sequence portion; and ii) a second cassette oligonucleotide labelled with an acceptor moiety (for example a quencher moiety), wherein the second cassette oligonucleotide does not comprise target specific sequence and wherein the second cassette oligonucleotide is between 1 and 5 nucleotide bases shorter than the corresponding first cassette oligonucleotide; c) initiating the primer extension reaction thereby generating (if the relevant target polynucleotide is present) a complementary sequence to the relevant first oligonucleotide primer, such that the relevant second cassette oligonucleotide is less able to hybridise to the relevant first cassette oligonucleotide, whereby a signal is generated; and d) detecting the signal that is generated,