The double photon emission of an electron in a constant crossed field has been calculated in [1]. By calculating the process of polarised single-photon emission, it is shown that the double-photon process can be unambiguously separated into two- and one- step subprocesses, also known as sequential and simultaneous double-emission. It is found that the assumption used in simulations of neglecting additional electron spin effects is valid to within a few percent, however the assumption that the two-step process is dominant becomes questionable for shorter background fields.