The number of muons is one of the key observables in the analysis of extensive air showers from ultra-high energy cosmic rays. Several experiments, which together cover a large range in primary energies, report the observation of an excess in the number of muons over the expectation from air shower simulations. In this work, we extend the catalogue of muon densities by the measurements that were carried out at the Haverah Park Array. We calculate the corresponding Haverah Park muon scale with respect to post-LHC hadronic interaction models, as defined by WHISP. We shift the original Haverah Park energy scale to the energy scale of the Pierre Auger Observatory by matching the spectra of the two experiments to one another. Comparing the measurements we find that the muon content measured at Haverah Park is not compatible with the one measured at the Pierre Auger Observatory. In particular Haverah Park measurements are compatible with the predictions from composition measurements and models.