A few points need to be made here:
1) If your engine is a "common rail" type (I could be wrong, but I think all Freelanders are common rail) you cannot run on a mix containing more than maybe 10% vegetable oil in the summer. These are far too sensitive to fuel viscosity.
2) If your engine isn't of a common rail variety but instead has a mechanical distributor pump (200tdi, 300tdi, TD5, BMW M51), the mix you can get away with in a single-tank scenario varies.
In the current temperatures, 50% vegetable oil / diesel mix is OK. In the summer I run 2/3 vegetable oil. You will probably need to go down to 1/3 or less vegetable oil once the temperatures drop below 0C. This applies to at least 300tdi and M51 engines.
300tdi is prone to injectors coking up. You'd do well to get yourself a spare set and when it starts to smoke horribly, swap them out and leave the dodgy set in a tub of redex for a few months until the new set gums up, and then swap them around. M51 doesn't have this problem. Mixing with petrol will make this problem worse due to it burning a little hotter.
P38 (M51 engine) - expect to have to change the lift pump in the tank every 3 months or so, so cut an access hatch under the back seat to get to it easily - otherwise you'd have to drop the fuel tank out every time (i.e. hours vs. minutes to change the pump).
If you have a 300tdi or a M51, get a fluid-fluid heat exchanger between the fuel filter head and the fuel filter. It will vastly prolong the life of the fuel filter and the injection pump. IIRC TD5's fuel line is routed through the cylinder head, so this isn't as important on those.
Vegetable oil will dissolve standard diesel seals made of nitrile rubber very quickly (weeks at most). This will cause the seals to shrink and perish, and turn into black dust which will clock things up. This is why when you first switch to vegetable oil the filters clog up very quickly. Viton rubber is much more resistant to vegetable oil (it won't perish and turn to dust), but it will still shrink a bit. This will eventually cause the fuel pump to leak and lose pressure and you'll have to change it. With a decent Bosch pump, however, this may well take over 50K miles, but budget for a £1200 bill for reconditioning the injection pump every 50K miles or so.
Considering all this, running on fresh vegetable oil isn't really worth it when you factor in the injection pump replacement costs and the relatively modest savings on the fuel cost (remember you still have to mix it with diesel. Used vegetable oil at 50p/litre is a much more sane proposition, but if you are going to do this on any worthwhile scale (you're allowed 2500 litres/year before you have to register and pay duty) you will need a settling tank and a filtering rig to filter down to 1 micron.
And yes, it'll smell very distinctly even when you've filtered it to 1 micron. It'll be very obvious and noticeable, possibly with a slight increase in smokyness especially if you run > 50% vegetable oil.
Black diesel (waste engine oil filtered down to 0.5 micron, then mixed with regular petrol/diesel) is an option, but unlike vegetable oil it is liable for full fuel duty+VAT, which makes it less worthwhile.
