There are no Duty Free concessions for Spain as it is part of the EU. You can bring back as much as you wish duty paid alcohol and tobacco as you can convince customs that it is for your personal use and not for re-sale.

You cannot buy duty free goods when travelling within the EU. However, in some countries such as Spain, the duty is much lower than the UK so you may wish to bring back tobacco or alcohol products that you have paid the duty. These must only be for your own use (including gifts for other people.

If you are bringing in alcohol or tobacco goods and HM Revenue and Customs have reason to suspect they may be for a commercial purpose, a Customs officer may ask you questions and make checks, for example about:

the type and quantity of goods you have bought
why you bought them
how you paid for them
whether all your goods are openly displayed or concealed
how often you travel
how much you normally smoke or drink or
any other relevant circumstances.

You are particularly likely to be asked questions if you have more than:
3200 cigarettes, 200 cigars, 400 cigarillos, 3kg tobacco, 110 litres of beer, 90 litres of wine, 10 litres of spirits, 20 litres of fortified wine (such as port or sherry).
The officer will take into account all the factors of the situation and your explanation.

If they are satisfied that the goods are for a commercial purpose they may seize them and any vehicle used to transport them, and may not return them to you.

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