A false comparison really. Channel Island gas is LPG derived, not natural gas. The unit cost of LPG (everywhere) is closer to electricity unit prices, so your gas unit prices are about double mainland natural gas prices.
As to the average, the domestic average annual use in a gas heated house is as stated earlier in the thread, ie 20,500kWhrs of gas and 3,300 kWhrs of electricity. Smaller houses less, large houses more. Personally I think 20,500 is excessive for even a moderately energy efficient average sized house.
You can see typical annual costs by using a comparison website.