So I've installed my new Avid juicy 5's but have a lot of excess cable
so what's the easiest way to cut them,and anything i should watch out for

Hose.

Make sure you have new olives to reseal them. I find cutting the hose with a stanley knife works a treat, without needing to rebleed the brake. Unbolt from lever, cut, fit new olive and insert, rebolt. Easy.

I think the Avid instructions document this pretty well.

^^ Would that apply to hopes too? My front has a slight bit of a leak on the caliper end after fitting braided lines

I blunted 3 stanley blades trying to cut my Avid Hose's it's tough stuff.

The big long razer sharpe kitchen knife went through them mighty well however.

Tinsnips worked well for me, Nice clean cut

Little hose cutter (like a cigar cutter).

Anyone know where to get an avid juicy 3 olive & insert (google fail to locate a UK source)

CRC
http://www.chainreactioncycles.com/SearchResults.aspx?Search=avid+olive
http://www.chainreactioncycles.com/SearchResults.aspx?Search=avid+barb

Have to ask, but the fact that they're marked as 05/06 is irrelevent then?

Is irrelevant, all the brakes use the same ones. You can recycle them if you're really desperate, but you risk stripping the master-cyclinder threads by having to overtighten to get a used olive to seal.