Thanks Jonathan for your help. I thought I would add the following for what it is worth.
These are a couple of Australian Boer War bottles with my Tobruk bottle.
I have included them to illustrate the colour of their covers. These bottles date from 1899-1900.
I believe the Tobruk bottle and its cover to be a re issued item from stores dating from WW1. This bottle was issued to the original owner in 1940.
I have realised that I have forgotten much of what I knew about water bottles years and years ago. Your comment about string attachment reminded me about that point and other details such as them being designated P’03 Mk6 and that British bottles early in WW2 changing to green enamel etc etc.
Previously I mentioned that the top seam bottles may be a late WW1 design.
On reflection I realise that another example of a Gallipoli bottle that I know of is seamed top and bottom and has a woollen felt cover much the same colour as my Tobruk one. (A lesson for me. Always ponder your answers before committing yourself. I am a terrible gas bag and often get into trouble for talking too much.)
Australian issued bottles in WW1 definitely had the green/grey-green covers as well as the colours you mentioned in your previous post. I have seen a green cover date stamped 1918. Also Australian troops like New Zealander’s would have been reissued from British stocks as necessary and therefore would have carried a variety of colours and designs.
I know British soldiers often had lighter coloured covers on their bottles.
I seem to remember seeing light coloured bottle covers in the shops in New Zealand when I was there 25 years ago.
I guess different places in the Commonwealth produced different items, not to mention the differences between manufacturers within the one country.
My final photo just for interest is of an unissued Australian made WW2 cover with its stamp relatively clearly seen.