It looks like I'm siding with most folks here, as we generally round up, and usually try to keep it around 5%. The only exception is if the MENU clearly states that service (not tip) is excluded, and then we resort to American customs. Clearly, Yvette's cannot possibly include service in their rates, but, L' Auberge Gourmand becomes a pricier proposition, but I'll respect their statement.

As an aside, in a strange land I ask try not to ask either Brits (I never tip) or Americans (I always tip 20%) for guidance. Doesn't always work out, though.