can anyone tell me if cable ties are ok for securing the wiring loom, or would i be better of (in regards to the SVA:mad putting in p clips or the likes

Cable ties should be ok,all the cars i've seen go through SVA have used them.

I got cable tie holders from a company called bluebeehive,they are realy handy and can be either riveted/self tapped or even glued.

http://www.bluebeehive.com

Site isnt that clever so 01437 890708 for a catalogue,they also sell termials/fuses/wire/heatshrink tubing and just about all you need for wiring incuding cable ties and tie holders.

Oh nearly forgot,blinding prices too

I have heard of SVA fails because a bunch of wires was secured around a bottom chassis tube with a cable tie. I think it was said that the cable tie could be worn away and fail in time. Much better to follow Bob advice and use chassis mounted saddles. My advice would be to run all your cables in then slip some split flexable convoluted tubing over the cable bunches then secure it, tubing is cheap and easy to use and makes a neat job.

cable ties should be perfectly ok if they aren't in any area where they could be damaged (i.e a lower chassis tube) and therefore release the cables.
the neatest and cheapest method i've seen is to use the rivet on saddles (black) which 'vehicle wiring products' sell. p-clips are ok but expensive.