Hi,
Over the last two weeks I have noticed that there is a very loud squeal every now and then when I take off.

The noise usually goes away by second gear and always goes on a gear change.
It has on occasion lasted up to fourth

I drive a 2004 1.2 Stilo

I'd say the most likely cause is the alternator drive belt.

Try a quick squirt of silicone spray while it's squeezing, if it stops it a new belt will be needed.