According to the AA the size is 23 square inches. One of those Sam Browne reflective belts should be ok.
http://shop.theaa.com/content/driving-in-europe
[color=rgb(0, 0, 0)]New regulation – motorcycles – effective from 1[sup]st [/sup]January 2013 [/color]All drivers and passengers of a motorcycle over 125cc or a motor tricycle over 15 KW/h must wear reflective clothing when riding their vehicles. In the event of an emergency stop, the reflective clothing still needs to be worn. The ‘reflective clothing’ must have a minimum reflective surface of 150 sq. cm (approx 23 sq. in.) in total either in one piece or in several pieces, and must be worn in the upper part of the body (between the neck and the waist). A fine will be imposed for non compliance.
Whilts trying to find out some more info I came across this
http://en.wikipedia.org/wiki/Sam_Browne_belt
Sam Browne belts were originally intended fo carrying swords.
http://shop.theaa.com/content/driving-in-europe
[color=rgb(0, 0, 0)]New regulation – motorcycles – effective from 1[sup]st [/sup]January 2013 [/color]All drivers and passengers of a motorcycle over 125cc or a motor tricycle over 15 KW/h must wear reflective clothing when riding their vehicles. In the event of an emergency stop, the reflective clothing still needs to be worn. The ‘reflective clothing’ must have a minimum reflective surface of 150 sq. cm (approx 23 sq. in.) in total either in one piece or in several pieces, and must be worn in the upper part of the body (between the neck and the waist). A fine will be imposed for non compliance.
Whilts trying to find out some more info I came across this
http://en.wikipedia.org/wiki/Sam_Browne_belt
Sam Browne belts were originally intended fo carrying swords.