An alternative -- but pricey -- means of obtaining lounge access if flying DL is to get the Amex UK Platinum card. There is currently an OK sign-up bonus if you can meet the minimum-spend requirements, and the card also offers some restaurant credits at selected restaurants in the UK and abroad, so the hefty annual fee might be justified for the first year. Coincidentally, the Amex Centurion lounges are located in the DL terminals at both LHR (T3), and JFK (T4). Current Amex offer here:

https://www.americanexpress.com/en-g...platinum-card/

("Our biggest ever welcome offer for a limited time only: Earn 40,000 Membership Rewards® points + £400 Amex Travel Credit + A chance to win tickets to the 2025 Wimbledon Championshipswhen you spend £6,000 in your first three months of Cardmembership. Offer ends 27 August 2024. Terms Apply. 18+, subject to status")