Amazon have very confirmed they are withdrawing free super saver delivery on items under £10, unless they are media items such as CDS/DVDs/Games etc. This means buying a small item for under £10 can incur delivery costs as much or even more than the item itself.
An easy way to get around this is if you buy a media item along with the small item at the same time, this qualifies for the free delivery. So just buy a cheap CD and you will gain free delivery, saving up to £6 on some items for delivery. In the long term, it may be best to buy amazon prime for £49 a year and have the added benefit of unlimited free one-day delivery on millions of eligible items.