I am getting a whistling squeak from front wheels, possible off side, when travelling on a straight but slightly left handed curved road, around the 30-40 mph. Skoda couldn't find a problem, but it is infrequent. Any ideas?

Could be CV/wheel bearing related. If this is the case it will probably deteriorate to a degree where it's noticeable all the time. 

 

I had a similar problem but with a clicking noise at the front. Turns out the bearings/CVs needed to be re packed with grease. 

 

Also check for stones in the brake heat shield but this is unlikely. Might also be a small stone in the brake calliper itself