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Political advertising, in the wider sense of ads that seek to influence public policy, is forbidden on television and radio. That means campaigning organisations have to use other means of getting their message across. Similarly, political parties may not promote themselves through TV advertising in programme breaks although they are allowed to publicize their messages through tightly-controlled party political broadcasts.
In non-broadcast media, political advertising, in both the party political sense and the wider sense, is allowed but the ads must comply with the CAP Code. The only exception is for ads that are aimed at influencing voters in elections or referendums: they are exempt from the CAP Code.
Political advertising on TV and radio
The ban on political broadcast advertisements comes from the Communications Act 2003 (it also existed in the earlier legislation on commercial broadcasting). The intention, of course, is to prevent well-funded campaigns from using the powerful broadcast media to gain unfair political influence....
http://www.cap.org.uk/cap/news_events/news/2006/Its+political+but+is+it+correct.htmWe could use some of that here. The UK also bans the broadcast of exit poll results until the polls close.
Thailand appears to ban pre-election public opinion polls.
http://www.nationmultimedia.com/Election2005/news/news.php?news=02/02020501.htmIn Canada (2000), the media was banning public opinion polls during the last few days of election campaigns. I don't know if that's still the case; I think their courts may have heard this and thrown it out.
In France, the findings of public opinion polls may not be published during the week before a ballot.
http://www.freeindiamedia.com/current_affairs/26_april_04_current_affairs.htm