Calling all armchair generals! Boudica's Last Stand.

[Nathan Ross]

“The Britons, flushed with success, advanced to give him battle...”

There's also the mention (in Agricola, I.5) of 'armies intercepted' (intercepti exercitus), which presumably refers - in a poetic plural - to Cerealis's expedition.

I agree with Michael that neither quote specifies an ambush: it sounds more like the Britons, having already taken Colchester and hearing of Cerialis advancing on them, moved out to block his route. This could have happened quite close to Colchester itself, and possibly Cerialis didn't accurately estimate their numbers until it was too late to extricate his force from encirclement. I think this would count as an 'interception', but perhaps the Latin word has other connotations.