Kind of surprised it has cordite. It usually wasn't used in rifle ammo after 1915ish.
That cartridge is not a reload. Primers used by reloaders are usually silver coloured. There's nothing odd or particularly unusual about the bullet either.
A MK VIII bullet would be a 175 grain boat tail. A MK VII from W.W. I used a flat based bullet.
Greenwood and Batley also used GBF and 'G' on their stuff. It's possible they were loading 'left overs' for the commercial market in 1949.
There's a pretty extensive list of what they made here. No Mk VIII listed. Odd considering they were working on ammo assorted until 1958.
http://www.dave-cushman.net/shot/303headstamps.html
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