ozmacca - The Regiments of Foot Guards in the British Army have actually lost their regimental numbers, which were in use during the Napoleonic Wars. The grouping of buttons denote the regiment's seniority. Grenadiers - 1; Coldstream - 2; Scots - 3; Irish - 4; Welsh - 5. You could say seniority = number, but the British Army always refers to Guards regiments by title (often as initials, such as 1/WG = 1st Battalion, the Welsh Guards).

Likewise, numbers are rarely used to denote Line Regiments, although there are very few left which have not been so amalgamated that their number looks like a winning lottery combination. I think there are still the Royal Scots (1st), Prince of Wales's Own (Yorkshire) Regiment (14th), Royal Welch Fusiliers (23rd). As with Guardsmen, titles are always used e.g. 1/DWR = 1st Battalion, the Duke of Wellington's Regiment.

In the last few years, the Armoured (cavalry) Regiments have also lost their numbers. There used to be a profusion of "Fraction Cavalry" e.g. the 14th/20th Hussars. The 16th/5th Lancers were the only one where for some reason the senior regiment on amalgamation had the higher number, they were often referred to as the "Vulgar Fraction".

I'm sure there must be a site out there somewhere which lists present and past British Regimental marches, I'll see if I can find it. As you might have guessed from the amount of b*ll I am spouting, I was once in uniform, in the 2nd Battalion, the Yorkshire Volunteers (2/YORKS), a now defunct Territorial Army unit. Its regimental quick march was, yes you've guessed it, "On Ilkley Moor bar't Hat".

Teribus - I don't know about the Scots Greys wearing hodden grey during the (English) Civil War. One interesting detail - the song, "All the Blue Bonnets are bound for the Border" dates from the Bishop's War of 1639 - 1640, which immediately preceded the ECW. When Charles I tried to impose an episcopacy and a new prayer book on Scotland, the Scots Covenanters formed a large army and invaded England; they captured Newcastle-upon-Tyne before Charles gave in. This army was issued with blue bonnets as a distinguishing piece of uniform.