If you are a UK national planning a holiday to Spain this summer then your status as a citizen of the EU is unchanged. This means that if you hold an EHIC card you will still be covered for essential medical treatment, and you can enter Spain with a UK passport with no special provisions.
After October 31st, assuming that the UK has left the EU you must be aware of possible changes. We strongly recommend that you have travel insurance that provides adequate medical cover. In addition you may be required to have a minimum of six months validity on your UK passport. A visa will not be necessary for short trips to Spain - however that may change so keep up to date with the news.
If you are planning to 'over-winter' here on the Costa del Sol and stay form more than 90 days then a visa may be required. At the time of writing we are seeking clarification from the British Embassy, but you may need to seek advice. We will be providing updates as soon as we have new information to share.