I haven't used amazon.uk but have used amazon.com. So, I don't know if the policies are the same.
Over the past 3-4 years, I have ordered a number of books from amazon. I haven't been charged any local taxes or custom duties. I think if you look at the Pak Customs Tariff
(may not be the most up to date) page 229
, it lists the custom duties on books as 0. Special books/documents like music sheets, maps etc. have some custom duty.
For some of the shipments I have had to pay no extra money. For others, a nominal amount like 20 or 40 rupees at most.
I think sometimes they are charged handling fees (many books; big package) by Pakistan Post (because once the shipment came to Pakistan, at the very end it was delivered by our local post).
Last time I ordered books from Amazon.com was in April, 2014. Since you are ordering from amazon.uk, so hopefully your package will arrive quicker. For me, some of my shipments were late by about a month. So, I switched from standard to expedited shipping. Even then, occasionally the books arrive later than the estimated date. However, none of my shipments have disappeared. Eventually all shipments have made it to me, some sooner, some later. Amazon's customer service was excellent. It has happened a couple of times that my package hadn't arrived even 2 weeks after estimated date. Amazon refunded my money on their own. When I later informed them that the books had arrived, they charged me for the books but waived the shipping fees (very nice of them, hope people don't abuse this policy).
As I said, amazon.com won't ship electronic items to Pakistan. I don't know policies of amazon.uk. Even if they do ship to Pakistan, I think Pak Customs will charge some duty (I don't think its amazon's job to clear customs). Also electronic items are more risky than books. More chances of the package disappearing. Sorry can't help you with info about electronics because I have never ordered any.
EDIT: I don't think amazon uk delivers electronics etc. to Pakistan. Have a look at their restrictions page for international orders direct from amazon.