Restoring yellowed lego back to white

Tippex?

As you mention hydrogen peroxide I assume you're aware of Retrobright?  It should work on Lego (it's ABS) but there's a question mark around long-term structural integrity.

I doubt there's anything you'll have just lying around that can 'clean' it.

Anyone had any success with houshold things?

Not if it's yellowed, no.  I tried all kinds of things from dishwasher tablets to IPA and even vodka.  Nothing worked as well as 6-10% Hydrogen Peroxide.   Hydrogen peroxide works well even at quite low concentrations, but it's worth sorting it into batches dependent on how yellowed it is.

My fridge had yellowed badly and I t cut it, made a big difference. Not convinced it will work on Lego tho

I just read baking soda and white vinegar might work so giving that a try now. Its been soaking in that for about an hour

I've had success with the hydrogen peroxide method. Was good enough that on a large flat surface that had partial sun damage you could no longer see the previously very strong line.

Yep UV and hydrogen peroxide. It's a chemical reaction that restores the colour, it's the bromide fire retardants that cause it to go yellow. Don't leave it in too long though as that kills the Lego.

Does it work on that horrible Scotland kit?