Higher costs of receiving parcels from abroad within the UK have sometimes come as a surprise so here is some information that some customers have shared with me overtime.

royalmail.com is a good place to get all the details and  this snapshot might be handy.

I'm sorry to say that we are unfortunately unable to mark the shipped items as gifts. The costs charged by the Royal mail are in addition to our shipping label cost of $13USD

Seems then all parcels with value of over 15GBP would incur a handling fee of 8GBP PLUS VAT

from Royal mail:

Our handling fee To make sure you get your item as quickly as possible, we pay HMRC any Import VAT and/or Customs Duty charges on your behalf. We then send you a “Fee to Pay” card, showing how much you need to pay before you can receive your item. The amount you need to pay includes our £8 handling fee. This covers the costs for clearing the item through the customs process and presenting it to Border Force.

here is a link with more info: 

https://www.royalmail.com/personal/receiving-mail/pay-a-fee/customs-charge