It would be worth doing a search of the unlocking board, there have been previous threads asking this question. Unfortunately, unless you are going to be in a position to use the phone in the UK on the local network you are going have a problem getting the phone unlocked through the network. Please see this link: How do I unlock my phone if I am not a Vodafone UK customer?
Your options will be to try and get the phone unlocked through the many unlocking services in Portugal, make a return to the seller or ask the seller if it is possible to request the unlocking from Vodafone.
