In a very small update on the forum, UK2000 has announced they have made Gatwick Extreme and Luton2020HD compatible with Prepar3D v5. They have shared several previews of the airports in both v4 and v5 to show how the products look differently in each sim. The new installers are available from your UK2000 account.
The top image on the left shows Luton in Prepar3D v4, the one on the right in v5. The images below show Gatwick in v4 on the left and v5 on the right.
You can purchase Gatwick Extreme for £16.99 and Luton2020HD for £18.48 here.