Bob is correct.
If you get the latest sealing glands that are currently coming on new lights, they have a larger/different threading than the old ones so your lid and ballast would need to be re-drilled and have the threads retapped.
The new ones look like this: (image shamelessly stolen from the Salvo website)
The other option is to get in contact with Corey Smith at Halcyon Tech Services and ship your light to him (in High Springs FL, USA) and have him update it to the latest sealing glands. If that's out of the question but you still want the newest version of the sealing glands, perhaps someone in the UK would be willing to drill out and retap the threads in your lid and ballast.