Thanks everyone,
The results of the postmortem came today and he died from an abdominal aortic aneurysm which basically means his main artery ruptured near his kidneys, I had a look on Google and in 2009 the NHS started a screening programme for it as 4 in 100 men die from it and by March 2013 every man over 65 should've received an invitation to go along.
Dad never received one and if he had then they'd have found it and treated it.
We're trying to find positives and the main one is that he wouldn't have known anything about it and at least it happened in his own home, the undertaker knows of one man who died from it whilst driving and killed a family travelling in another car.
It's also kickstarted my husband into being more healthy, some of the causes can be being overweight and having high cholesterol both of which he has, Dad didn't have either, he must've been one of the unlucky ones.
Thanks again for the messages, they mean a lot.xx