  Bound states in the continuum (BICs) have been thoroughly investigated due to
their formally divergent Q-factor, especially those emerging in all-dielectric,
nanostructured metasurfaces from symmetry protection at the $\Gamma$ point
(in-plane wavevector $k_{||}=0$). Less attention has been paid to accidental
BICs that may appear at any other $k_{||}\not =0$ in the band structure of
supported modes, being in turn difficult to predict. Here we make use of a
coupled electric/magnetic dipole model to determine analytical conditions for
the emergence of accidental BICs, valid for any planar array of meta-atoms that
can be described by dipolar resonances, which is the case of many
nanostructures in the optical domain. This is explored for all-dielectric
nanospheres through explicit analytical conditions that allow us in turn to
predict accidental BIC positions in the parameter space $(\omega,\bf{k_{||}}$).
Finally, such conditions are exploited to determine not only single, but also
double (for both linear polarizations) accidental BICs occurring at the same
position in the dispersion relation $\omega-\bf{k_{||}}$ for realistic
semiconductor nanodisk meta-atoms. This might pave the way to a variety of
BIC-enhanced light-matter interaction phenomena at the nanoscale such as lasing
or non-linear conversion, that benefit from emerging at wavevectors away from
the $\Gamma$ point (off-normal incidence) overlapping for both linear
polarizations.
