Challenge to the Forum - identify these four!

[bumpermark]

This is a modern copy of an old photograph that I have acquired. I would appreciate any information that anyone could give me regarding the makes and models of the four motorbikes shown.
I have no idea at all, so please don't expect me to give out the answers at the end of the post.
Here are a few clues, the bike on the far left has been registered HF 6, this series being issued by Wallasey County Borough Council in April 1913
Second bike in from the left is registered CM 1108, series being issued by Birkenhead C.B.C. and is possibly a Rudge?
Third and fourth bikes have no readable emblem information on them.
I have no idea if these are military despatch riders or postal workers, perhaps someone has seen this photograph before?
Please let me know what your thoughts are........

[mini-me]

The one in the middle is Rudge, on the right Douglas, left hand one is Rover or Humber[I think] and the fourth one looks like another Rudge.

[R]

Its maybe also worth commenting that they all appear to be kitted out identically,
including goggles and those rather distinctive hats.
Some sort of military unit ? - although on their privately owned bikes ?

Such teams often participated in Trials events - long distance road rides, very popular in that era (1920s) so its not impossible this was the prelude to one ?

[cardan]

Left to right Rover, Rudge (single speed - not the more common Multi), Douglas, Rudge.

The 2 3/4 hp (350cc) Douglas was one of the two main bikes of WW1, the other being the Model H Triumph.

Cheers

Leon

[bumpermark]

http://www.ebay.co.uk/itm/192164038307?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649

Thank you to everyone who contributed to this thread - at least I been able to identify the motorcycle models for sale in the photograph.