Having come upon this thread, and read through it, I thought that the topic was Distinction cloth rather than braid.James_C #56 has accurately described the Mercantile Marine Uniform as prescribed in the Order in Councils, however several members seem to be confusing this with company livery which can easily be identified by the absence of MM cap badge.
Livery is a distinctive uniform worn by servants, employees, officials etc. There is no restriction on the amount of livery braid worn by a cinema commissoner, bus conductor or merchant ship's officer, only subject to the whim of the employer. As few ships remain under the British flag I presume the uniform rules, if any, of the flag state are applicable and the MM badge will be conspicuous by it's absence.
Distinction cloth being the coloured cloth, originally velvet, worn between the braid to show department - Originated by the RN I believe then adopted by, and now used exclusively by, Merchant marine, of whatever company or flag.