Thanks for the advice, based on threads I've read the glow plugs do seem to be a common issue but I was discounting this due to the ambient temp (which you have pointed out is incorrect), but also because it always starts when the Li Jump starter is attached. Would the boost from the jump starter help the glow plugs heating cycle?

Its a 2005 E53 BMW X5 30d, I purchased it from the original owner with 10K kms back in 2006.. its go a few more kms on it now ~ 310K.