  The WFCAM Transit Survey (WTS) is a near-infrared transit survey running on
the United Kingdom Infrared Telescope (UKIRT), designed to discover planets
around M dwarfs. The WTS acts as a poor-seeing backup programme for the
telescope, and represents the first dedicated wide-field near-infrared transit
survey. In this paper we describe the observing strategy of the WTS and the
processing of the data to generate lightcurves. We describe the basic
properties of our photometric data, and measure our sensitivity based on 950
observations. We show that the photometry reaches a precision of ~4mmag for the
brightest unsaturated stars in lightcurves spanning almost 3 years. Optical
(SDSS griz) and near-infrared (UKIRT ZYJHK) photometry is used to classify the
target sample of 4600 M dwarfs with J magnitudes in the range 11-17. Most have
spectral-types in the range M0-M2. We conduct Monte Carlo transit injection and
detection simulations for short period (<10 day) Jupiter- and Neptune-sized
planets to characterize the sensitivity of the survey. We investigate the
recovery rate as a function of period and magnitude for 4 hypothetical
star-planet cases: M0-2+Jupiter, M2-4+Jupiter, M0-2+Neptune, M2-4+Neptune. We
find that the WTS lightcurves are very sensitive to the presence of
Jupiter-sized short-period transiting planets around M dwarfs. Hot Neptunes
produce a much weaker signal and suffer a correspondingly smaller recovery
fraction. Neptunes can only be reliably recovered with the correct period
around the rather small sample (~100) of the latest M dwarfs (M4-M9) in the
WTS. The non-detection of a hot-Jupiter around an M dwarf by the WFCAM Transit
Survey allows us to place an upper limit of 1.7-2.0 per cent (at 95 per cent
confidence) on the planet occurrence rate.
