The attachment you are using may not be securely attached. Remove and re-attach, ensuring it is locked in place.
The Dualit Hand blender is designed for intermittent use; you may have used it for over a minute. Allow it to cool and try to use it for shorter periods of time.
The food chunks may be too large; try chopping into smaller chunks. You may also need to adjust the speed selection.
Try using a deeper bowl and dip the blending stick into the mixture before turning the power on. Start on a lower speed and gradually increase as you blend. Ensure the mixture does not go above the MAX mark on the front of the shaft.