Use code "paypal20" to get 20% off the LIST PRICE (not basket price) for spend over 100GBP.
Overall discount will vary based on your choice of items but I just got about 7% off the basket price for my order :)
One thing to note is that you'll have to use either Paypal's exchange rate or Wiggle's which reduces the savings somewhat. Overall I found it to be better than not using the code at all.
T/C's here: http://www.wiggle.co.uk/h/option/Vouchers
Make sure u don't buy anything you might want to return as they send it back to the UK and charge you $15!