What to use in litter tray?

For the lat 4 years we've always used puppy pads to line Annie's litter tray and have never had a problem. Yesterday she decided to shred the puppy pad apart whilst I was at work - cue me having major anxiety about a blockage and leaving work early to monitor her. Thankfully she's fine and I don't think she ate any but now I need to use something different to line her tray as I don't want to risk it.

What do you guys use to line the litter tray? When we first got her we used back 2 nature paper litter but stopped as she used to dig it and make a mess.

I'm in the UK so please don't suggest US exclusive brands :)