David McCullagh says it’s definitely time for him to move to radio.

“In the space of a week before the summer, women approached me at random on two separate occasions and told me I looked much better on telly.”

One of these unsolicited verdicts on his real-life appearance was delivered just outside the RTÉ campus in Montrose, Dublin.

“I went in and told the make-up department. They were delighted,” he says.

As I meet the journalist, presenter and historian (57) in a hotel lounge not far from Montrose, he’s limbering up to swap the Six One television news for Radio 1’s Today with David McCullagh – and poised to publish his latest book, From Crown to Harp.

Completed with the aid of a “really, really handy bout of insomnia”, the book covers the 28-year period in which the Anglo-Irish Treaty was undone, with McCullagh exploring three decades of fractious negotiations and much-contested shifts in symbolism.

He cites an October 1921 cartoon in British satirical magazine Punch in which an Irish nationalist, asking if the inn he finds himself in is the Harp, is told it’s the Crown and Harp. “But I don’t think you’ll find it any less comfortable for that,” the innkeeper replies.

“It sort of encapsulates the British attitude of ‘all we’re asking you, all we’re asking you, is to give us our symbol, and it will have no practical difference. And to an extent that was true, to an extent they were lying through their teeth.”

Evolving expressions of identity from stamps, coins and passports to flags and anthems are covered, though especially fun to consider now are the diplomatic exchanges over recognition of the Irish president in official toasts.

David McCullagh: 'I think 10 hours of me on air a week is probably enough.' Photograph: Nick Bradshaw/The Irish Times

“It seems kind of arcane and