I used to have a lot of items sent to me from the US and this was how it worked - it may have changed now:
1. Import duty applied to value of goods (where applicable).
2. VAT applied to value of goods PLUS above import duty PLUS postage - yes the thieving swine charge VAT on postage paid in another Country!

3. Post Office handling charge.
My understanding is that UPS, FedEx, DHL etc work out the charges and pay Customs accordingly. This avoids delays in delivery but guarantees that you will have to pay the charges.
However, if the package is sent by United States Postal Service it is then assesed by our postal service. This has 2 possible outcomes:
1. Due to staff shortages etc they don't assess the package and it comes through without a charge.
2. They do apply the charge. If this happens make sure you check their calculation - I have had a few occasions where the US valuation was converted to GBP on a straight 1 to 1 ratio. Also I have been charged higher rate VAT, which applies to clothes, for items that were clearly not such.
Over several years and several hundred deliveries I would estimate the the parcels that go through the PO get charged about 60% of the time - less around the Christmas period.
As for the handling fee based on what the PO charges and how long it must take to assess a package that must be one of the best paid jobs in the country!
Oh and before anyone asks I used to deal in film and TV props.
BTW certain items are exempt from charges:
Printed matter - it has to be clearly marked as such on the package and declaration.
Company samples.
Gifts up to the value of £15 (I think that's still the correct amount). Of course having a less than £15 valuation on the package and an invoice for $400 inside doesn't help.
Although the Postal Service assess the charges the package still goes through Customs first and they are the ones who will open anything they feel may have a 'fictional' valuation on it. Back in the day when I was importing they were very sharp on 'grey' imports of items from big manufacturers. At the time I knew several people who were importing Star Wars toys (don't laugh - it was BIG business) and the Customs had a full US price list and opened virtually every shipment. However, I doubt that they could tell the difference between most cues, although the 'ivory' issue also comes to the fore with high end cues.

[ This message was edited by: laz1957 on 2009-03-19 12:55 ]