Gold isn't traded in different qualities on the commodities markets. Only 'pure' gold (24ct) is traded. Further, international commodities markets don't trade in sterling, they trade in dollars. And they don't trade in grams, they trade in troy ounces.
So even British sources will quote gold prices according to those standards. The Financial Times, for example, is currently reporting the price of gold as $1512.30 per 100 (troy) ounces at the end of today's trading:
http://www.ft.com/markets/commodities
The CNN website uses the same standards, but includes silver as well:
http://money.cnn.com/data/commodities/
(Again you need to remember that it's 'pure' silver that's being traded, not the stuff that your silver jewellery is made from).
If you want to try some conversions, here's the percentage of pure gold in the various carat standards (rounded to 1 decimal place)
22 ct = 91.6%
21ct =87.5%
20ct = 83.3
18ct = 75%
15ct = 62.5%
14ct =58.5%
10ct = 41.7%
9ct = 37.5%
8ct = 33.3%
1ct =4.2%
Also 1 troy ounce = 31.1034768g
'Fine silver' is almost pure (99.9%) but 'sterling silver' only contains 92.5% silver content.
Chris