Re: British .303
Well Crunch.....indeed, the Rifle No. 5, Mark 1 was known as the "Jungle Carbine" and was used exclusively in the Pacific Theatre.
Unfortunately, I don't think that's what you've got. A few years ago, these Jungle Carbines came on the market and proved to be highly popular. Demand exceed supply, so some unscrupulous importers started cutting down the older No.4, Mark 1 and No.4, Mark 1* and sold them as the real Jungle Carbine.
The reason that I think yours might be a fake is that it has the wrong front sight, no bayonet lug, no flash hider, and a barrel band around around the front of the stock (which the original didn't have).
If it were genuine (and I could be wrong on the above), it's value would be:
Exc. - $500
V.G. - $400
Good - $300