  We present an XMM-Newton analysis of the cataclysmic variable T Leo. The
X-ray light curve shows sinusoidal variation on a period P_x equal to
0.89^{+0.14}_{-0.10} times the previously spectroscopically determined orbital
period. Furthermore, we find a signal in the power spectrum at 414 sec that
could be attributed to the spin period of the white dwarf. If true, T Leo would
be the first confirmed superoutbursting intermediate polar IP). The spin
profile is double-peaked with a peak separation of about 1/3 spin phases. This
appears to be a typical feature for IPs with a small magnetic field and fast
white dwarf rotation. An alternative explanation is that the 414 sec signal is
a Quasi-periodic Oscillation (QPO) that is caused by mass transfer variation
from the secondary, a bright region (``blob'') rotating in the disc at a radius
of approximately ~9 Rwd or - more likely - a travelling wave close to the inner
disc edge of a dwarf nova with a low field white dwarf. The XMM-Newton RGS
spectra reveal double peaked emission for the O VIII Ly alpha line. Scenarios
in the IP and dwarf nova model are discussed (an emitting ring in the disc,
bright X-ray spot on disc edge, or emitting accretion funnels), but the
intermediate polar model is favoured. Supported is this idea by the finding
that only the red peak appears to be shifted and the `blue' peak is compatible
with the rest wavelength. The red peak thus is caused by emission from the
northern accretion spot when it faces the observer. Instead, the peak at the
rest wavelength is caused when the southern accretion funnel is visible just on
the lower edge of the white dwarf - with the velocity of the accreting material
being perpendicular to the line of sight.
