They have been making this charge on items under £30 for a little while now, I is very obvious when you order, in very large print, so there shouldn't be a surprise.
I suspect the customer services were ill equipped to deal with the volume of small items. We certainly ordered all sorts of small items for local collection.
Boots are still offering free instore collection, not sure how long that will last, it can't be worth their while. Ordered a very small item that was just a few pounds, came in relatively huge box that could have held hundreds of the same item.
We tend to use eBay for small items.
Amazon increased their delivery charges some while ago ( and they don't make it very obvious)