Oxford BioMedica, one of the UK’s best--known biotechnology companies, has rejected a takeover approach by GeneThera, the agricultural diagnostics specialist, saying the suitor was not a “credible bidder”.

The takeover approach comes a month after Oxford BioMedica’s shares lost more than half their value in one day after TroVax, the company’s leading drug, failed to meet targets in a renal cancer study.