Take it out of the plastic bag and heel it in somewhere until you can plant properly, use a torch to see what you are doing if necessary.

Thanks - think I will perhaps take a half day off work, if not will try above.

Presuming that it is a bare root specimen I would just plunge it into a bucket of water for a couple of hours and then keep it in a cool dry(ish) place - it shouldn't be active at the moment and will survive the few days until you plant it. The risk of heeling it in is that you could damage the roots in the double-handling involved.

In the past I've soaked them for a couple of hours then wrapped it in an old towel and kept it damp until I could plant them.

Roses are not dormant yet because it's been very mild. That's not good for bare root roses being dug up prematurely

Undo the packaging asap, and dig a hole big enough to take all the roots and cover them completely with damp soil. When you remove the rose I'd inspect it. Make sure you have a decent looking root system and at least 3 sturdy stems. if not ring up Parkers for a replacement. They are not the greatest people to buy roses from as has been my past experience.