This is from JAR OPS 1.295:
(c) An operator must select at least one destination alternate for each IFR flight unless:
(1) Both:
(i) The duration of the planned flight from take-off to landing or, in the event of in-flight re-planning in accordance with JAR-OPS 1.255(d), the remaining flying time to destination does not exceed six hours,
and
(ii) Two separate runways [(See JAR-OPS 1.192)] are available and usable at the destination [aerodrome] and the appropriate weather reports or forecasts for the destination aerodrome, or any combination thereof, indicate that for the period from one hour before until one hour after the expected time of arrival at [the] destination [aerodrome], the ceiling will be at least 2 000 ft or circling height + 500 ft, whichever is greater, and the visibility will be at least 5 km.
So if you have a flight under 6 hours, two separate landing surfaces at your destination airfield and the weather is within the limits described above, you do not require a destination alternate (ie you can use your destination as an alternate).
I'm not saying it's good practice but I believe it to be legal. I know of at least one airline which was considering adopting this policy at MAN but decided against it.