You may be wondering why that usually hyperactive segment of the Twittersphere marked "Political correspondents/TV" is silent on a day of such political interest. Here's Laura Kuenssberg, chief political correspondent for the BBC News Channel, with her one and only tweet so far today:

The answer, for BBC broadcasters at least, lies with the BBC Trust. Its Referendum Guidelines (PDF), published in November 2010, read:

2.2 Polling day:

• No opinion poll on any issue relating to the referendum may be published.
• There will be no coverage of any of the referendum campaign issues on any BBC outlet.

Note "any BBC outlet": the corporation's purdah applies to the internet and social media sites such as Twitter as much as it does to television and radio. The same rules apply for regional, local and general elections.

But what about other news broadcasters such as ITV, Channel 4 and Sky? Here it is not so straightforward. All three are overseen by Ofcom and, for the record, rule 6.4 of the Ofcom Broadcasting Code reads:

Discussion and analysis of election and referendum issues must finish when the poll opens. (This refers to the opening of actual polling stations. This rule does not apply to any poll conducted entirely by post.)

But this guidance is for television and radio output only: Ofcom does not regulate new media.

So, in theory, the likes of ITV News's Lucy Manning, Sky News's Joey Jones and Channel 4 News's Cathy Newman could be tweeting away as usual, so long as they avoid the TV studio between 7am and 10pm. In practice, however, the broadcasters know such inconsistency won't wash. Hence, a self-imposed exile.

For the same reason, they demand (but don't always get) due impartiality from their blogging and tweeting correspondents.

There are no such guidelines for the duly partial print media, regardless of outlet.