However, such advertising operates beyond the boundaries of most advertising regulation. It is not required to prove its claims and can mislead by inaccuracy and ambiguity, exaggeration, omission or otherwise. It is sometimes sanctioned - witness the case of the "demon eyes" poster at the 1997 election - but not always. In other words, it's an unholy mess.
So we should welcome this week's news of a report into the funding of political parties by the Institute for Public Policy Research, the Downing Street-linked think tank (see news, p4). At last someone has realised the "part in, part out" approach to political advertising is good for nobody. It is confusing for the general public, it brings advertising in general into disrepute, it is bad for poster contractors and, in the context of an overall drive for higher standards in public life, it is bad for political parties too.
So what's the way forward? According to the IPPR, it is to back an extension of state funding to political parties via free billboards to parties in the same way as they are already allowed party political broadcasts.
All well and good, you might argue, but consider the voter apathy that reigns now. Only 59 per cent of the population bothered to vote in the last election in 2001, the lowest since the 1918 general election, and I'll bet a fraction of that bothered to watch any party political broadcasts.
Treat posters in the same way and I predict even further voter apathy.
The IPPR also argues the case for putting COI Communications in charge of supervising poster buying by political parties during election campaigns.
On one level, this makes eminent sense. COI suspends its activity during elections and therefore has to cancel numerous prime sites. In its capacity as an expert media planner and buyer, COI could police the sector against some of its previous sins - including the twin practices, coined by the Conservative Party, of booking sites under false names and the donation of space to parties by friendly advertisers.
But look closer and the proposal appears dubious. COI's role as a neutral precludes its staff being drawn into the political battle.
It would be more sensible, perhaps, to start again from scratch. First, all political parties publicly acknowledge that political advertising is, in effect, a form of propaganda which should not be judged by the rules that apply to other forms of advertising.
Second, compose an independent committee which reports directly into Parliament and oversees a new specific code of practice designed to self-regulate all party political advertising - both the media used and the messages themselves.