the Court of Appeal has discretion to admit any evidence "in the interests of justice". But from what we know about the "Aga burns" grounds it's difficult to see what coherent argument there is to say this shows the conviction is unsafe
Look at it this way, Jonathan, if the Aga burned Nevill and the police 'didn't' move Nevill after entry then this must be what happened if JB is guilty......
JB enters WHF, Nevill hears him and goes to the kitchen where he is knocked out and falls against the Aga, JB kills everyone else and then sits and waits for an hour or two for Nevill to come round, then he allows Nevill to get up before struggling with him until he ends up on the chair/scuttle before shooting him in the head, then JB heads for home.
Alternatively....
JB enters, shoots Nevill and June in the bedroom, chases behind Nevill as he goes to the kitchen shooting him in the arm and shoulder, JB then bashes Nevill and he falls against the Aga, JB shoots everyone else and then sits and waits for Nevill to regain consciousness only to bash him again until he ends up on the chair/scuttle, JB shoots him in the head then leaves!
You see the problem, Jonathan? Why didn't JB just shoot Nevill to death while he was lying against the Aga and get to hell out of there? Doesn't make sense to wait for Nevill to come round does it? Gee whizz, how did JB know that Nevill would regain conscience 'at all' that night?
Its just implausable nonsense! JB would have shot Nevill to death as soon as he fell against the Aga!
No jury on earth would convict JB on such a scenario, cant you see that, Jonathan?
Besides, the evidence suggests that Nevill hadn't been shot at all while lying against the Aga, there is no blood spatter around that area or on the Aga.