What is the best way to advertise my new fencing business (north west UK)?

[Rufus]

I'd say; start building awareness though advertising in the local newspaper in the small classified ads as regularly as you an afford, especially during periods of gales force winds or just after. Maybe look at Letterbox marketing (leaflets delivered inside your local free sheet newspaper) normally very cost effective. People looking to get work done hang onto such leaflets for future reference.

Create a facebook page for your fencing business and promote it on your business cards, ads, vehicle ect. Create a blog on your website and start blogging about fencing/repair/maintenance/Durability and these days sustainability.

For more instant work have you checked out tradesmen websites that connect customers looking to get work done with tradespeople (http://www.ratedpeople.com is one that comes to mind)
Or
Some of the big diy stores and supermarket chains allow you to promote your business to their customers, (check out their websites or talk to the local manager of the store). On this score you could also approach the wood yards supplying fencing direct to the public as they maybe asked if they know someone who can do their fencing work (provide something the wood yard can give to such customers).

Once you have those first few contracts make sure you've got an ad board you can leave outside the property where you are working to promote yourself to neighbours. Ask for testimonials for your work and post them on your website.

All the very best with the venture.