Times when one rival TV channel advertises on another

I've noticed in the last few days an advert for Steph McGovern's new lunchtime show on Channel 4 is going out on ITV.

It got me wondering how common this is or has been over years gone by?

Less common that it used to be. C4 prob do this a couple of times a year? A key stipulation is that they can’t advertise the specific time it’s on.

Naga Munchetty was actively promoting people to catch up on Who Wants To Be A Millionaire by going to the ITV Hub, during Saturday's BBC Breakfast!?

Is there a reason why they can't?

Hollyoaks sometimes advertise on ITV too.

I think the time cannot be shown due to it taking away viewers from the channel the advertising is on.

Of course back in the day when your local ITV company was providing the adverts for Channel 4, you would quite often hear something like "Brookside starts shortly on Channel 4, You're watching Central, time now for World in Action" or whatever at quite a few junctions.

Yes, and full blown trailers. Just the same as BBC 1 and 2. Of course today a trailer simply becomes an ad when it's shown by another broadcaster (or in the cinema)

And obviously there’s a load of Sky Sports / BT Sport adverts on the terrestrial channels, and BT Sport adverts on Sky, and the other way round...

And indeed Central even had a combined ident featuring the cake and the C4 blocks for cross-promotion. Sadly I can’t find an example online at the moment.

And of course Channel 4 would have promos for ITV programmes, and when they were networked pointers to ITV programmes.

Though some bigger regional ITV companies used to occasionally put in continuity announcements for regional programmes. This is a Thames opt out on Channel 4, advertising Thames News 'starting soon on ITV':

I remember that ident, but like you, can’t find any trace of it online.

The ITV/C4 cross-promotions lasted beyond the years when ITV provided the commercials and Channel 4 was basically an “ITV2”. Do we know when exactly these stopped? Was it from the start of 1994?

ITV stopped supplying the ads on C4 on Dec 31 1992, and C4 started selling and transmitting their own ads from the following day, but there was still a financial safety net the ITV companies had to provide, so cross promotion in a reduced form continued until that expired. 1998 ish I think?