A metaphorical bomb hit the UK preference share market last week when insurance company Aviva announced, on the back of strong profits and the proceeds of asset sales, that that it would consider cancelling its "expensive" preference shares. Nothing unusual in that, you might say, except the particular preference shares referred to were issued in 1992 as "cumulative and irredeemable" and they have a coupon rate of 8.75% per annum. Most...