Right now. Semi-ripe heel cuttings of 4-6in side shoots are best. Don't take great long woody pieces as they won't root. Remove lower leaves and place in very gritty compost in terracotta pot. Put poly bag over and place in shade outside. Keep just moist and they should root in six-eight weeks. leave in pot though till spring (with bag off).

Or look around the bush, almost guaranteed to be self set seedlings - we remove all the time!

thanks for the info,what are (self set seedlings)

If you have a female holly that sets berries these will drop and produce baby holly trees. Otherwise you'll need ot take cuttings as per Fractal's info.

I have found quite a few little holly trees not even around where there is a holly.Is it possible the birds have dropped a berry in my garden..?

More likely that they have eaten the berry and the pooped out the seed. I love our holly trees, except when it comes to weeding around them, even gloves don't keep out the prickles from the fallen leaves.