Here's a rough way to look at it:
If you buy a sovereign for �110, you're getting just under one quarter of a troy ounce. So to get (nearly) a whole troy ounce you'd have to pay buy 4 sovereigns, which would cost you �440. On the other hand, you get a whole troy ounce by buying a Krugerrand for �248, so which are you going to buy?
If you'd rather have a precise answer, the sovereigns are priced at �478.26 per troy ounce, which is 1.93 times (i.e. nearly double) the gold price of the sovereigns.
Chris