In a speedy turnaround, the Spanish Ministry has issued a regulation exempting the need for non-EU citizens to require permission to acquire most properties, even if they are within militarily sensitive zones. The requirement still remains for acquisition within Rustic land, and therefore may still apply to ‘regularised’ properties with an AFO. The map of the sensitive zones is given below.
1.1. Due to Brexit on 31st December 2020, UK buyers are now non-EU citizens. Accordingly, under the Law 
8/1975, and the Royal Decree 689/1978 in Spain, as with most other non-EU citizens worldwide, UK Citizens may be required to obtain permission from the Spanish Ministry of Defence to purchase rural property in substantial areas of Spain that are held to be militarily sensitive. In addition to North Murcia and South Alicante and the area West of Sotogrande, these include much of the Balearic (Mallorca, etc) and Canary (Tenerife, etc) Islands.
1.2. This uncertainty can delay purchase by a number of months, which could put them at a disadvantage when offering against an EU Citizen. Sellers are less likely to accept a conditional offer that could take some time to conclude. You should confirm the situation with your lawyer.
