Vacuous really, there’s McGonagall’s initial, shocking versifier (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

An anagram (shocking) of R[eall]Y + THERE’S + M[cgonagall) (‘shocking versifier’ – see here and here ‘s his famously egregious poem – my husband was a Dundonian and he would have loved this one, as I did