You don't really think that things could be that simple, do you? After all, it's a Government department that you're dealing with! ;-)
Each type of clothing is categorised differently (and, therefore, may well have different rates applied). You need to consider what materials are used in the production of the clothing (and possibly whether it's for men, women or children).
Similarly there are lots of different classifications for jewellery.
Then, to complicate matters further, you need to remember that both VAT and Import Duty are calculated on 'CIF' value (which is 'cost, insurance and freight') and not solely upon the cost of the goods.
To do the job properly you need to find the 10 digit tariff code from here and then seek the relevant information for that code:
https://www.gov.uk/trade-tariff/sections
As you'll see (if you're brave enough to work your way through that lot), you need to go through several web pages just to get to the correct subheading and then read through hundreds of lines to find the exact description of the item.
However you can cheat a bit by getting the first 4 digits for clothing items from here:
https://www.gov.uk/classifying-textile-apparel
(There doesn't seem to be a similar link for jewellery. However it's not too difficult to get the full codes from here:
https://www.gov.uk/trade-tariff/chapters/71 ).
Once you've done that you can go here:
http://www.dutycalculator.com/new-import-duty-and-tax-calculation/
Section 1 is self-explanatory.
In Section 2, change 'Product Description' to 'HS Code'. Enter the full 10-digit code if you've got it, otherwise enter just the first 4 digits and take a guess (from the options offered) at the rest. Then use the next boxes to narrow down the description.
Enter your product value, complete Section 3 and click the big green button. (NB: Don't try it for just a single item as, if the value is less than £135, you'll see that no Import Duty is payable. You need to enter the figures for a whole consignment to obtain the correct duty calculation).