Look at notice
179E
Section 4.2.
If you have produced or used less than 2,500 litres of:
* any biofuel, or
* any other fuel substitute or additive
within the last 12 months, and/or expect to produce or use less than 2,500 litres in the next 12 months, you are an exempt producer and do not need to register with us and account for duty. However, there are simple record keeping requirements, which are described in paragraph 4.9.1.
Production includes the manufacture or processing of road fuel, and the setting aside of any product that has not been charged with duty, with the intention of using it as road fuel.
And under section 2.1
2.1 What are biodiesel, bioblend, bioethanol and bioethanol blend?
The law describes biodiesel as a diesel quality* liquid fuel that is produced from biomass or waste cooking oil:
* the ester content of which is not less than 96.5% by weight, and
* the sulphur content of which does not exceed 0.005% by weight, or is nil.
*diesel quality means that the fuel is a substitute for diesel rather than petrol.
'Bioblend' means any mixture that is produced by mixing:
* biodiesel, and
* heavy oil that has not been charged with the excise duty on hydrocarbon oil.
So, as long as you keep records of how much you use, you should be ale to use ANY oil in a "blend", as long as you chuck a bit of veg oil in at the same time.
Edit: forgot to say, there is clause which allows you to add Lubricants to fuel, and these will not attract duty. Section 2.3.