This is a rare RSM visor cap from the Irish Guards, one of the British Army's five regiments of foot guards. The five gold bands on the peak signify a WO1 rank, normally the RSM and the Superintending Clerk (a now defunct rank). 

It has minimal service wear. Marked a size 57. It is from the 1980s/90s. The cap has the classic Guards warrant officer look to it where the peak has been cut back and restitched so that it sits almost flush to the forehead when worn.