Facing TV Problems? Ask a TV Technician.
What all input types have you tried? (e.g. Sky box, DVD player, digital TV, etc)
Are all input types affected in the same way?
Ok, then the flickering is likely caused by external interference, perhaps from a nearby wireless device (e.g. cordless phone or wireless router), or fluorescent lighting, or from a bad power supply.
Try moving the TV to a different location and use a different power socket. Check if it works ok there...