Spandex, can you break down that £19? If you take off the RoyalMail's highway robbery £8 fee, there''s £11 left.
£11 VAT suggests that the whole package was valued around £62 - so in that case the gift process wouldn't have made a difference at all (as all it does is - at HMRC discretion - double the amount before they start applying VAT from £18 to £36 - and as there's no "allowance" you pay on the whole amount not the whole amount minus the £18 (or £36 if it's a gift))
Any packages marked as gifts should be of an occasional nature (that's HMRC speak for birthdays, wedding anniversaries, Christmas..) and HMRC have ways and means beyond your wildest imagination of finding out "stuff".
If you can prove (by means of an invoice included in the package) that the package including postage was valued lower, you can appeal to HMRC and if successful they will refund the overpayment - and if you get the whole VAT amount back, you can then appeal to RM to get the brokers fee back too. I've done both in the past and it was painless.