No Spanish army would be complete without a band of guerrillas in my opinion, and those from Essex have a fair bit of variety:
As with my 28mm efforts I tried to restrict myself to a predominance of a variety of browns rather than try to splash around too much colour:
The same figures double up for urban militia, which are still loosely-based but in a slightly tighter formation than the guerrilla units:
There is a common perception of guerrilla units lurking around French supply lines, ready to cut down stragglers or intercept communications. This is probably true for the most part and they played a vital role in continually harassing the French and inflicting some fairly substantial losses, and also augmenting allied intelligence with regard to French movements.
I remember being quite surprised to read about the deployment of Julian Sanchez's guerrillas on the British right or Southern flank at Fuentes de Onoro, however short-lived that deployment may have been. One of Sanchez's men rode up to the French to taunt them before the battle, but some British light troops apparently mistook him for a French officer and shot him. Sanchez was (probably not unreasonably) upset, and quit the field of battle.
The British did manage to subsequently convince Sanchez to redeploy behind the field of battle and defend some of the approaches to the town of Fuentes do Onoro. I personally find the episode interesting because it confirms the potential for guerrillas to be deployed in the line of battle, rather being relegated to skirmish games.