Worldwide, if securities regulators believe in one thing, it is the value of transparency. Sunlight, they know, is the best disinfectant. But sometimes in confusion they pull down the blinds. This has just happened in the US and, as a result, transparency in the market for corporate control is in danger. Unlike other regulators, the Securities and Exchange Commission has chosen – at least provisionally – to disregard equity derivatives and thus allow acquirers to use them to outflank the early warning disclosures that the US (and most other big countries) impose on the assembly of a potentially controlling block of stock.

For decades, the US’s takeover laws have required any person to disclose to the SEC and the market when he or she crosses the 5 per cent threshold in terms of the “beneficial ownership” of a publicly held company. Because the goal of these rules is to alert the marketplace to any incipient control contest, the SEC had always defined “beneficial ownership” broadly – at least until earlier this month.