  Around 16% of the solar-like stars in our neighbourhood show IR-excesses due
to debris discs and a fraction of them are known to host planets. We aim to
determine in a homogeneous way the metallicity of a sample of stars with known
debris discs and planets. Our analysis includes the calculation of the
fundamental stellar parameters by applying the iron ionisation equilibrium
conditions to several isolated Fe I and Fe II lines. The metallicity
distributions of the different stellar samples suggest that there is a
transition toward higher metallicities from stars with neither debris discs nor
planets to stars hosting giant planets. Stars with debris discs and stars with
neither debris nor planets follow a similar metallicity distribution, although
the distribution of the first ones might be shifted towards higher
metallicities. Stars with debris discs and planets have the same metallicity
behaviour as stars hosting planets, irrespective of whether the planets are
low-mass or gas giants. In the case of debris discs and giant planets, the
planets are usually cool, -semimajor axis larger than 0.1 AU. The data also
suggest that stars with debris discs and cool giant planets tend to have a low
dust luminosity, and are among the less luminous debris discs known. We also
find evidence of an anticorrelation between the luminosity of the dust and the
planet eccentricity. Our data show that the presence of planets, not the debris
disc, correlates with the stellar metallicity. The results confirm that
core-accretion models represent suitable scenarios for debris disc and planet
formation. Dynamical instabilities produced by eccentric giant planets could
explain the suggested dust luminosity trends observed for stars with debris
discs and planets.
