jim, now that you english burocrat can sleep peaceful since you're ok with the law [in italy we've been governed by mafia over the last 5 years so don't think it's a REAL prob if I run my car on bio,,,] I'd like to give you my suggestions [not that they're worth much more than 2p]:
1-you need to filter the **** at 20 microns or more if you can,,, but filtering it at 20 microns is quite difficult, let alone doing more,,,
2-better if you can find non-hydrogenated oil [kinda hard]
3-bacteria is quite a big issue with diesel/veg oil so you can't shelf it for a long time,,, I'd be worried to use some that waited more than 2-3 weeks,,,
4-water + disposed oil =
5-the only REAL issue I didn't overcome here is oil viscosity: our fine injectors don't like the thickness of the veg oil so the pump [Bosch VP-37 on our 110s] is stressed more,,, so if you need to rebuild the pump after say 1 year then all the savings go down the toilet,,, possible solutions I've thought:
-get bigger nozzles for the injectors, so the holes are bigger and the pump does less work to push oil,,,
-pour anti-diesel-freeze stuff at every fill up [you should still be saving],,, this stuff basically reduces diesel viscosity and therefore gelification on low temps,,, this means that at normal spring/summer temps it can get veg oil to normal diesel viscosity,,,
[this obvisouly needs to be tested for quantities/mixing etc.]
-just dilute veg oil with normal diesel and wait for the warmer temps to begin raising veg oil percentage [20°C+ at the moment in roma should do
]
-buy a kit like
this and empty your beloved wallet,,,