There is an unusually large amount of information on this campaign because Tacitus composed an historical biography of Agricola who was his father-in-law.
Let's Talk About Myths, Baby! | Greek Mythology & the Ancient Mediterranean
Instead, he tends to stick to the narrative, and I get the feeling that his account is more trustworthy because he's pulling this information from his father-in-law Agricola, who actually was in Roman Britain during this time.
By the end of the year Agricola had largely completed the conquest of Wales, bringing forces onto their island stronghold of Anglesey and forcing the tribe to accept peace terms.
Hence, although he would not live to see it, Vespasian's directives to Agricola set in motionchain events which saw the Roman Empire extended into northern England and southern Scotland for the first time.
In 77 AD he appointed Gnaeus Julius Agricola as governor of Britain and charged him with expanding into the northern Wales and even further northwards in Britain itself.