We've got a Hawthorn hedge at the bottom of the garden,
which shields us from a main road, and although its a lovely hedge,
Wouldn't swap it for a fence or anything, cos the little birds love it,
back to the subject,
Its realy bushy in summer but this time of year when its got no leaves doesn't give much privacy from the road,
So I was wondering would it be possible to plant Holly plants in with it,
and if its ok where can I buy some from.

Yes you can - after all Hawthorn and Holly live happily together in the wild in hedges so there is no reason why not. The best thing to do is choose spaces in the hedge where there is a natural break and plant there or if there is no break then try plant them in anyway and see how they go - if they need more light then you can always cut the hedge back a bit to allow some in. When planting just dig a hole and put some nice compost / manure in with perhaps some bone meal and the holly should romp away!

As for where to get them any decent garden centre should stock them. Where abouts do you live - that might give us some clues as to where to point! Personally I like the garden centre at Bamford - but you might not even know where that is :)

Thankyou for the advise I live in Sheffield,
but dont mind a trip out to a nice garden center.

Well Bamford is a good garden centre - just head towards Hathersage and keep going until you meet the junction at the old Maquis of Grandby pub (a ruined pub that is being left to fall apart..) go straight on at the junction (towards Shatton / Castleton) and you'll come to a bridge - the garden centre is just over the other side of it.

Failing that I'm sure there are lots of others who could recommend ones...

It might also be an idea to look into laying it - that will help close up any gaps between bushes and the ground as well. It is fairly straightforward to learn (if you are not too worried about the final appearance and technicalities!) and will create a stronger thicker hedge in the future. It would still be possible to intersperse holly too.
http://www.hedgelaying.org.uk/

It might also be an idea to look into laying it - that will help close up any gaps between bushes and the ground as well. It is fairly straightforward to learn (if you are not too worried about the final appearance and technicalities!) and will create a stronger thicker hedge in the future. It would still be possible to intersperse holly too.
http://www.hedgelaying.org.uk/

I love to see those properly "laid" hedges, a lovely bit of craftsmanship.

I have a fuchsia hedge that is still establishing, but I wish I had planted hawthorn to repel certain undesirable elements!

Volunteer training courses in hedgelaying are run throughout Sheffield in the winter months - if anyone is interested then Sally Pereira at SCC is the organiser - she can be contacted through SCC switchboard for more details.