Hi. If you've bought it in the Uk then all pine is kiln dried, so it should be ok - but obviously you wanted Aspen, not Pine, or you'd have bought pine. Where did you get the Aspen from? I don't know if cedar is used in the Uk or not - I don't think it is. Pro rep aspen is supposed to be ok. I use Fitch paper bedding - it's quite popular. Works out quite cheap too as you can only buy it in bulk (10kg or 20kg). I get the 10kg as it's a more manageable size. It lasts me about 6 months. It's like Carefresh but without the dust. Zooplus also sell organic hemp bedding.
Fitch Recycling - 10kg Single Bale Fitch Paper Bedding For Smaller Critters - Fitch Pet Bedding
Nests & Nesting Materials at zooplus: Hemp Bedding