I don't know about the flavour.
As long as you are using it with a base malt you can use up to ~50%, you don't need to get malted triticale or pre-cook it(see below). Also, I have no idea where you could find some in the UK; if you can find some flaked then try that.
PS: if you know where to find some please post a link here, because I am now rather interested in trying it too.
I currently know nothing about the falvours, but regarding the techniques I have found a reference. Brewing: New Techniques edited by C Bamforth Section 3.4.1 Unmalted Triticale:
"Most non-malt adjuncts do not contribute either enzyme activity or soluble nitrogen ... triticale goes beyond this specification ... Because of this and the low gelitinisation range of triticale starch(59-65C)... triticale could be used as a brewing adjunct at high ratios(<30-50%) ... furthermore, because of its low gelatinisation temperature, triticale can be added directly to the mash tun, without the need for a cereal cooker or second mashing vessel"