The Percentage of deaths in the UK compared to actual cases in actual fact will be way, way less. we don't know how many people have actually had it , as stated before because of a lack of tests. So conceivably , the figure could easily be 10, 20 times higher than reported.
however, we do know as a matter of fact how many have died from it. so that figure is right to use for percentage purposes, but if it used against a figure of 10 or 20 times more than the official figures , then the percentage will diminish drastically.