Returns on a Special Offer product?

I dont know whether this is the right place to ask, but I'd really like to find out.

I've used the returns process before with a couple of faulty products, so I know how easy it is to use, but I was wondering what the returns-value is of a product which was brought as part of a special offer deal.

ie, I receintly took advantage of the 3 for £10 deal, and now am unsure of keeping one of the items. Because it was part of this deal, what is the value of this product? If the original price was £6.99, could I ask for a replacement product costing that same amount (or one slightly more and pay the exact difference)- or would I be charged extra because the value of the returned item is less because it was brought in a sale? Does the replacement have to be something which was also part of that 3 for £10 deal, or could it be anything?

Could someone please explain to me, just to put my mind at rest. Thanks!

At a guess, i'd expect it to have to have been in the 3 for 10, or they'll refund £3.33?

With LH, you never know, they have excellent CS. Just email/live chat (when they're on) or even call.