The first rule of television - and the only one that everybody knows - is that there are no adverts on the BBC. Commercials are, of course, the wretched business of ITV, Channel 4 and the rest - the kind of broadcasters who, apparently, entice us to engorge ourselves with the occasional display of “junk” food advertising. Those who dislike the commercial message, and have no need to visit the bathroom in the middle of their favourite programmes, can escape to the haven of the BBC's output, where, of course, there is no sort of insidious advertising. Right?

Wrong. Increasingly, advertisers are being offered the chance to pay to promote their brands live during BBC programmes - flagship productions at that, such as Children in Need, Saving Planet Earth or live concerts on Radio 2 - and trusted presenters, such as Gary Lineker or Sir Terry Wogan, are naming brands in programmes in a way that commercial broadcasters would not be allowed to do.

Remarkably, ever so helpfully, this is spelt out on a BBC website - bbceventsponsorship.com, located conveniently at arm's length from the main BBC site. It spells out what the BBC offers sponsors - “visual and verbal credits on BBC One” and “money-can't-buy VIP invitations to First Night and Last Night of the Proms”. Sponsors who support Children in Need (last year Boots, BT and HSBC) are told that participating in the appeal gives them the chance “to showcase your brand within editorial content to mass audience on radio, on TV, and online”. In sponsoring Saving Planet Earth, HSBC received a package in which the bank was promised “contractual visual and verbal credits” on BBC One.

Now, with Children in Need, say, the BBC does not take cash from the sponsors - rather, they make a nice donation to the charity for the privilege of being named on air. Yet sponsoring charitable events is only part of it. The handy website reveals that Radio 2 live events are open to advertisers, with “verbal credits” on Britain's most popular radio station and “branding on the events page on Radio 2 website”. Up for grabs is a Phantom of the Opera broadcast in June and Andrew Lloyd Webber's Greatest Hits in September.

So, how much does the BBC generate from this activity, which sits not in its commercial business, Worldwide, but appears to be part of its public service division? Ah, Auntie won't tell you, that being commercially sensitive information. It might be £1 million a year, not much in the context of the licence fee, but money that still is otherwise not available for advertisers. And by charging less than a “market rate” for sponsorship, the BBC helps to drive down the price.

The obvious question, of course, is that there must be rules for this sort of thing. The first is the loophole that allows this activity to take place: the BBC is quite clear that it cannot take money from sponsors to help to defray the costs of programmes. But live events are another matter and here, apparently, a deal can be struck with a sponsor with respect to a live competition, such as Young Musician of the Year, which just happens to be shown live on television. So the difference between an event and a programme is moot.

The treatment of Sports Personality of the Year is an example of what can be done with this new go-ahead attitude. What was once a familiar programme has become an event. It was watched by a studio audience of 8,000, transmitted live to the nation - and sponsored last year by Robinsons, the soft drinks maker. For an estimated £200,000 Robinsons got “contractual visual and verbal credits on BBC One and Radio 5 Live” on a show fronted by Lineker and Sue Barker. That helped to pay for the cost of the event - sponsors often don't write a cheque that has “BBC” on it, but helping to pay for the venue hire, for example, is hardly much different.

ITV and RadioCentre, the body that represents all commercial radio companies, cannot quite believe it. ITV thinks that it couldn't get away with selling in-programme sponsorship as the BBC does. Ofcom rules are quite clear and say that “products and services cannot be promoted in programmes”. Yet the BBC is regulated, not by Ofcom but by the BBC Trust, which, two months after the first complaints from ITV and RadioCentre were made, is, finally, getting round to investigating.

Nevertheless, once the grandees of the Trust get to opine, they surely won't find it quite so complex. All they need to remember is the first rule of television: there are no adverts on the BBC. With that simple principle in mind, it is obvious that so-called event sponsorship is wrong. Viewers do not expect brands to be promoted in programmes, in deals that the BBC strikes with advertisers. Otherwise, why did they pay the licence fee in the first place?

Times Recommends

• Minister in talks with Saudis to protect creditors
• Premier Inn hits back in £29-a-room row
• Bankers hit back at 'populist' bonus supertax