Large colour lines / bands on screen

Hello. I've got a problem with my few years old TH42PX60 Panny plasma and I hope someone on here can help.

Recently some coloured lines have appeared on screen from top to bottom just over mid-way across the screen and it's extremely annoying to say the least. These lines seem to change colour from blue to yellow to red and appear to flicker as well. Sometimes the lines turn to black, showing a completely black band on screen. What is causing this? It is not interference and I've checked connections to the TV. They appear on both analog and satellite AV channels and they appear a few minutes after switching on the TV.

I've posted images for reference on imageshack (link included).

I've noticed the purple snakes issue a few times on my set but it wasn't too bad so I've not bothered to contact Panasonic about it but I'm worried that this recent issue with the coloured lines may be related? Does anyone think Panasonic would fix this issue for me even though the TV is a few years old now? I thought that a plasma should last a little longer that this as it was so expensive.

Any help would be greatly appreciated!

http://img41.imageshack.us/g/dsc00198p.jpg/