Unfortunately I failed to archive a copy of the article as I found it at that point, however the article then was a subset of the article as updated at 13:08 GMT a screencap of which can be found here in case they change it again. The BBC's URL for this article is <http://news.bbc.co.uk/2/hi/business/7362676.stm>.
The version of the article I saw this morning essentially consisted of the first three or four paragraphs, and some of the end section entitled "Global problem". Combining the first two paragraphs leads one to the conclusion that the BBC believe that the average family of four spends about £100 a week, however with a little further thought one quite quickly decides that in fact the £15 figure has arisen as part of a misguided attempt to make the 15% rise mentioned in the second paragraph more clear — an attempt that falters because the assumption that the initial price of a weekly shop was £100 hasn't been stated, and anyone reading enough of the article to realise that this has been done will reach the same conclusion from the later 15% figure anyway.
That's only the first thing to inspire alarm in the article however, moving on to the second paragraph we discover that this 15% figure has been produced by comparing the cost from one year to the next of a basket of 24 "basic" items. This is a fairly standard and well understood method of tracking something akin to the actual cost to consumers of inflation. The same method is, for instance, used to calculate the CPI which is the official measure of consumer inflation. This method is very dependent on the particular objects that have been selected to make up this basket and it is at best rather dodgy of the BBC to fail to give an indication of how the objects in question were selected. The revised BBC page (as given above) improves on this situation by listing approximately half of the items included in the basket.
Fortunately the BBC do acknowledge the source of their data as being mysupermarket.co.uk although they are unable to give a direct hyperlink to the data as mysupermarket don't have it available on their website. I emailed the press contact at mysupermarket and asked them for a copy of the data that the BBC article was based upon and was rather surprised when they replied within a couple of hours. The reply consisted of an excel spreadsheet with comparison data for the dates 21st April 2007 and 21st April 2008 and text which looks remarkably like sections of the BBC News article that I was originally interested in. Indeed it looks to me very much like the BBC have cut and pasted sections of a press release and then massaged them very slightly to make their story, and without applying much critical thinking on their part either. For instance the source of the confusing headline statistics appears to be this paragraph from the release, assuming it is similar to the email which I received:
At present, the price of a staples food basket compared to last year has gone up by an average of 15% just on these 24 staple items. Applying these increases, if a family of four spends on average £100 on their weekly shop, and this is increased by 15%, this equates to a price hike of £780 per year.
— Personal email from mysupermarket.co.uk
I shall write more about the actual research in a further article. Whilst, I think, there is a role for the BBC to publish information like this collected by corporations they should avoid making this a means of getting press releases distributed widely for free, and instead they should apply some critical thought to the information that they have been sent, and possibly contrast it against other data in the field. This article in particular adds to this lack of criticality with a throwaday comment in the first paragraph about "The highest food costs since 1945" which may well be true, but for which they provide no supporting documentation but appear to assume that it is a well known fact. They do include, in their side-bar, a link to an article entitled "The cost of food" which consists entirely of mostly short-term graphs and diagrammes the criticisms of which I could fill an entire other article with. Their article Q&A: Rising world food prices is somewhat better, but doesn't address the kinds of questions I'm criticising the initial article about.
Going on from here I feel I should complain directly to the BBC, but whilst I've gone through my thoughts in this article it's not entirely coherent or directed. Do you think I should send the BBC a link to this article, or get someone to revise it and turn it into a fairly coherent set of complaints to send to them?