For those of you close to East London, a quick walk along Whitechapel Road (A11) may pay dividends. I got an EN compliant bomber style flourescent jacket (nicely padded too) in a little shop there for £25 (down from £35 normally). They were also selling waistcoats for £8 as well as yellow T Shirts with reflective bands ...
As Circuit Basher says, the standard for such jackets is contained in EN471:1994. This lays down the allowable colours and the width and placing of the reflective stripes. Both International Yellow and Rescue Orange (as they used to be known) are allowed.
Cursory inspection of the Mustang jackets website shows that they're not EN compliant (yet). (At least, that's my reading of what they say and in support of that view, there's no obvious sign of the flourescent stripes).