Yes, you should be able to run on a 50/50 mix, depending on what type of seals you have on the fuel filter, normally after 500 mile the fuel filter should be changed, as the veg oil will loosen the crud left by Diesel, but if you add 1 ltr of white spirit, this will help keep the veggy oil thinner so you could get away with 60/40 in favour of veggie oil.
If by some misfortune, you get a slight leak from the fuel filter, just top up with Diesel, and this will fix any leak.
Even better if you can find a garage which sells Biodiesel as this has been through various stages to remove water and glycerin.
I run my truck on BioDiesel @ 90p a ltr. and find it quicker and a slightly better mpg. In the winter I run on 80% bio and 20% diesel.
People can smell you coming a mile off, a mobile chip fryer
Have a great journey