In theory, off-grid enewable energy systems can still qualify for feed-in tariffs. This is because, as with a grid-connected system, they will be replacing or avoiding the use of fossil fuels. In fact, if an off-grid renewable energy system is used instead of a diesel generator the carbon savings will be higher than if it replaces grid electricity.
However, the problem is that there is currently no DC generation meter that meets the requirements set out by OFGEM in their document "Feed-in Tariff: Guidance for renewable installations". A previous version of this document stated explicitly: "As set out above, a meter has to be approved to appropriate standards. It is our understanding that, at the current time, there are no DC meters that meet the FIT metering legislation requirements." This statment is now missing, and the document and various offical websites are now unclear about off-grid metering, which is not ideal.
It may be possible to get FIT payments by using an accredited inverter and AC meter in an off-grid system, but this conflicts with the fact that for smaller appliances (e.g. lighting) it is more efficient to have 12 volt DC appliances supplied directly from the DC battery store. In an off-grid system it is less efficient to run these small loads as AC appliances through an inverter. So it's a bit of a mess really.
If a suitable meter does at some point become accredited, you would need to have a system installed by an MCS-accredited installer (accredited under the Microgeneration Certification Scheme) and sign a declaration that "it is my intention to use any and all electricity generated by my FIT Installation and that I fully understand that any electricity generated but not so used will not be eligible for FIT payments" (as in the above OFGEM document). Then you should be able to contact any mandatory FiT supplier (i.e. any large electricity supplier) and get them to pay you the generation tariff for the electricity produced by your system, as metered by a generation meter.
CAT is not involved in the administration of the feed-in tariff (FIT) scheme, so to find out if a DC off-grid meter is in the process of becoming accredited (or if there is one out there and we've missed it) you will need to contact the bodies that are paid by the Government to undertake administration & support for the FIT scheme. These are the Microgeneration Scheme, the Energy Saving Trust, and Ofgem.