Hi guys — this is a great topic and I'm surprised it hasn't come up here before.
The finer details of the insignia and the various embellishments with increasing rank for the full dress tunics for the Footguards regiments are not immediately apparent until you look closely at the different ranks. The main four groups are: Officers, Warrant Officers, Senior NCOs, Junior NCOs & guardsmen.
Marc, your top pic is the badge for the Scots Guards, with the Star of the Order of the Thistle.
This is the version for the Coldstream Guards, with the Star of the Order of the Garter:
On the uniform:
Note the Warrant Officer uniform embellishments of the gold lace to the collar, the two bands of gold lace around the cuffs and the gold lace that edges the cuff flaps and the buttonholes on the flaps. WOs also have gold piping around the edges of their shoulder straps; NCOs and guardsmen have plain white piping around the shoulder straps.
The same uniform, with bearskin cap, worn by a WO2 CSM of the Welsh Guards
The back of the tunic
I can't find a decent pic with the details of the Colour Sergeants full dress tunic being worn, so here's one on a hanger instead (!). I'll add one later if I can find a good one.
Note the plain dark blue collar but with badges in bullion. Senior NCOs also have gold lace to the button holes on the cuff flaps but, unlike warrant officers, there is no gold lace edging to the cuff flaps or around the cuffs. There is similar gold lace to the buttonholes on the rear skirt of the the tunic. Junior NCOs and guardsmen have white-laced buttonholes and plain white embroidered badges on collars and shoulder straps.
Irish Guards colour sergeants with guardsmen (note also the red shoulder sashes worn by the sergeants)
A non-CSM appointment WO2 (left, front), a Colour Sergeant (right, front), a Lance-Sergeant (appointment given to full Corporals in the Footguards regiments, right, back, with three white chevrons and plain cuffs/collar) and, just visible, a Sergeant (left, back, with three gold chevrons and gold buttonholes on the cuff flaps). Note that the senior NCOs and the WO wear white gloves, the junior NCO does not. The sergeants' sashes are red, the WO's sash is crimson. Oh, and the Warrant Officer wears a sword!
The special badge of the Colours, surmounted by a Crown with crossed swords below, is specific to the appointment of WO2 CSM. Non-CSM WOs2 wear the standard crown/wreath insignia of the WO2 rank (as in the pic above).
For a Colour Sergeant, the badge is worn over the three stripes of a sergeant in gold lace on the full dress tunic and a smaller version is worn over chevrons created in outline with gold soutache in No1 Dress (blue patrol tunic). The equivalent ranks of Colour Sergeant / Staff Sergeant in non-Guards regiments and corps wear a crown above three chevrons.
Similarly, the BIG bullion embroidered Royal Arms badge, worn above
the elbow, is specific to the WO1 RSM appointment
and other WOs1 wear the more usual Royal arms badge of the WO1 rank (most commonly seen in the regimental bands).
The Big Badge worn over four
chevrons, again, above the elbow, is unique to the appointment
of Garrison Sergeant Major, London District and was re-instated in 2011. Prior to this, the GSM wore the same Big Badge as the RSMs of the various Footguards regiments.
GSM with RSM:
The current GSM London District:
If you're interested, the UNIFORMOLOGY site is a great resource for good pics of badges of the British Army. I won't steal their images, better that you go take a look:http://www.uniformology.com/BADGE00.html