+ 1 on Graeme's comment.
It's just a transit plug to stop dirt.
It had me confused for a while too as it looks too complicated to be "just" a plug.

As a BEWARE comment, be very careful about leaning the strut assembly vertical against anything.
I did & the whole strut fell over - straight onto the pipe connection, damaging it !

It took me hours to dis-assemble the strut top to make a reliable replacement pipe connection.

PS Although I know BWI are an OEM supplier to Land Rover & took over the original Delphi business that made the OE struts, I've not been impressed with the damper settings on the BWI struts I fitted last year.
They are definitely not specced. as the OE struts.
It's not the fantastic limousine ride quality I was expecting or have experienced in other similar, but lower mileage cars on OE struts. I think they're slightly too firm. Not bad, but not optimum. Paul,
2001 Discovery 2 TD5, 211,000 miles & climbing
2006 FFRR TDV8 Vogue 145,000 miles & climbing
Member of Midland (Land) Rover Owners Club, www.mroc.co.uk

That's interesting. Thanks Pawl and Graeme.

I guess the obvious question is that the original brass screw in collar is a different size to the new BWI one as far as I can tell.

That required either the removal of the standard collar on the hose or cutting it off entirely. Then the challenge of fitting the hose through the new collar, once the white tab has been removed.

Any suggestions as to how to proceed with this?

Thanks.

I just unscrewed the hose, 12mm spanner, changed the strut and screwed in the old connector still on the hose to the new strut. You don't have to take the wheel arch liner out either. Plenty of room if you have a short 12mm spanner.

I tried removing the threaded section from the new strut and it seemed slightly too small to fit in to the old strut. It disappeared into the threaded hole, including the flat sided section you are supposed to tighten.