I'll be sitting watching a DVD, and all of a sudden, Sky cuts in and takes over the TV. This tends to happen a lot if Sky Sports, for instance in on Sky at the time, and goes to a commercial break, but it can also happen on any TV programme, and at any time.

Is Sky sending some kind of signal down the scart cable, and is there any way, like chopping one of the pins on the socket, to get rid of the problem?

Did look at disabling Scart control on the picture setting menu on the Services button, but that will obviously degrade the picture quality.

My setup is, Toshiba LCD TV connected by HDMI to Sky, and by scart to my DVD recorder, with Sky connected by scart to the DVD recorder to allow me to record in RGB, with both Sky and DVD recorder connected by optical cable to my amp.

Why would turning off SCART control degrade the picture? If you are talking about the pin 8 signal then all that does is tell the device on the other end of the lead that it is on. And also whether the signal it is sending is 4:3 or 16:9.

The ONLY consequence of turning it off is that you will have to select the appropriate SCART input on the destination device manually and also switch between 4:3 and 16:9 yourself. There should be no effect whatsoever on picture quality.

The only effect it might have is if it also switches off the pin 16 RGB signal but I would think that is unlikely. That is far more likely to be under the control of the Video out control (ie where you switch between RGB, Composite or S-Video) which ought to be entirely separate from SCART control.

It sounds like your TV is the culprit, maybe thinking the Sky box has just powered-in so swaps to it. Can you disable auto-input select on the TV?