We decided to fire up the LG Surround sound last night and watch some things. First time in months we'd done so. I couldn't believe the time lag between the surround sound and the TV itself. It was okay when we muted the TV audio but surely we shouldn't have to do that? It took a good few minutes of adjusting the settings to get it in sync. Is this a usual problem? Both the TV and Surround Sound systems are 2011 models.

I wouldn't have thought it a good idea to have the TV audio on when using your surround system. Either or would be the way to go. Surprised the Sound system didn't mute the TV automatically...
Sorry can't help on the specific model you have....

You should not use the TV speakers at the same time as the surround system. The surround system replaces the TV speakers, not add to them.

And by lag what exactly do you mean? To me that means sound from device A appears after sound from device B. It would be normal for the sound to appear from the TV after it appears from the surround system.

This is because the pictures take a bit longer to process than the audio. So the telly delays the audio a few milliseconds to synch them back up again.

Obviously the surround system has no idea how long the TV it's being used with takes to process the pictures. So most decent ones have a variable audio delay built in. It is often called lip synch.

So turn off the TV speakers and use only the surround speakers. Having both on at the same time is only likely to degrade the sound quality, rarely does it improve things.