Try UPS it costs about £60. You can book and pay with your credit card over the phone and if done before (I think) 12 noon and they collect the documents before (I think) 2 pm, they will deliver next day in Spain.
They will give all the information you require over the phone. My only problem was that the bank in Spain, to whom I sent the package, refused to take delivery at 6 minutes to 2.00pm and UPS had to return the next day.
UPS has an online tracking system and so you follow your package on it's journey and know the minute it is delivered.