  We are entering the era in which observations of protoplanetary discs
properties can indirectly probe the presence of massive planets or low mass
stellar companions interacting with the disc. In particular, the detection of
warped discs can provide important clues to the properties of the star-disc
system. In this paper we show how observations of warped discs can be used to
infer the dynamical properties of the systems. We concentrate on circumbinary
discs, where the mass of the secondary can be planetary. First, we provide some
simple relations that link the amplitude of the warp in the linear regime to
the parameters of the system. Secondly, we apply our method to the case of TW
Hya, a transition disc for which a warp has been proposed based on
spectroscopic observations. Assuming values for the disc and stellar parameters
from observations, we conclude that, in order for a warp induced by a planetary
companion to be detectable, the planet mass should be large ($M_{\rm p} \approx
10 - 14M_{\rm J}$) and the disc should be viscous ($\alpha \approx 0.15 -
0.25$). We also apply our model to LkCa 15 and T Cha, where a substellar
companion has been detected within the central cavity of the transition discs.
