This is a colour variation of the Black Watch tartan.
T. Smibert produced a book entitled, 'The Clans of the Highlands of Scotland' in 1850 which is widely regarded as an accurate source for the tartans illustrated within it. Smibert had access to the patterns of Wilson's of Bannockburn who had been weavers 'since the '45'.
The ‘ancient’ has nothing to do with the age of the tartan it merely denotes that dyes have been used that may give a better impression of the colours of the sett before modern dyes were used.
MacLachlan Old, Modern
‘Old and Rare Scottish Tartans' (1893), contains a Maclachlan Tartan very different to the one most often seen today
MacLachlan Old, Ancient
The tartan closely resembles that of Campbell of Loudoun, except for the red stripe