DFS4020 | Technical Guidance: What are Duty Free Spirits (DFS)?
From HM Revenue & Customs · Duty Free Spirits Guidance
Duty Free Spirits are normally, plain British or unsweetened imported, spirits (ethanol) of not less than 85.5 % alcohol by volume. Any other spirits can be received as duty free providing the trader can make a satisfactory case, eg vinegar makers may receive low strength feints or low strength spirits extracted from beer.