Southbank Centre, LondonThe hero of the children's animated TV series is on top form in a riotous adaptation that gets the squirrels singing and screaming I must confess that it took me a while to get into the children's cartoon Hey Duggee. So scrambled was my brain when fatherhood began that I would often stare at it slack-jawed as the multilayered writing and smart gags flew over my head. This musical theatre versi…