Anyone know where I can buy inkjet ink for direct fabric printing in the UK?

To my knowledge, there is no such ink ever invented. Inkjet inks have to be thin to form small enough droplets to work with the printhead properly. Trying to print on fabric would only come out as smudges, because of the wicking action of the fibers. Most fabric printing is done by a process called silk screening. The process and equipment to do this is pretty expensive.