  Anisotropic properties of single crystals of SrPt$_{3}$P were studied using
London penetration depth and electrical resistivity measurements. The upper
critical field, $H_{c2}(T)$, was determined from four-probe electrical
resistivity measurements for three orthogonal directions of a magnetic field
with respect to the crystal. The London penetration depth, $\lambda(T)$, was
determined from the magnetic susceptibility of the Meissner-London state
measured using a tunnel-diode resonator technique. Whereas $H_{c2}(T)$ and the
normal-state $\rho(T)$ are practically identical for all three magnetic field
orientations, the London penetration depth shows significant unidirectional
anisotropy. The low-temperature $\lambda(T)$ is exponentially attenuated when a
small excitation radiofrequency magnetic field, $H_{rf}$, is applied along the
$c"-$direction, in which case screening currents flow in the $a"b"-$ plane,
while for the other two orientations, $H_{rf}\parallel a"$ and $H_{rf}\parallel
b"$, the London penetration depth shows a much weaker, $\lambda(T)\sim T^{2}$,
variation. Such unusual and contrasting behavior of the two anisotropies,
$\gamma_{H}\left(T\right)=H_{c2,ab}/H_{c2,c}=\xi_{ab}/\xi_{c}$ and
$\gamma_{\lambda}\left(T\right)=\lambda_{c}/\lambda_{ab}$, imposes significant
constraints on the possible order parameter. Although our measurements are
insufficient to derive conclusively the superconducting gap anisotropy,
qualitatively, order parameter with two point nodes and a modulation in the
perpendicular direction is consistent with the experimental observations.
