Your post is offensively stupid.
I left England in December 2019. Not the 1970s.
The anti-Irish remarks were made directly to me, not overheard, and, given the total ignorance of staggering numbers of English people of the most basic facts about Ireland, would, in any case, not have involved any discussion of Irish current affairs.
These people were not Irish, don’t be silly. In some cases an anti-Irish remark was followed by them priding themselves on having voted for Brexit and being canny enough to have applied for an Irish passport via a grandparent. Often then followed by a complaint about how long the process took.
Their Irish grandparent does not make them Irish. It certainly doesn’t appear to have given them the remotest knowledge of or interest in Ireland, or any insight into their own motivation for kneejerk anti-Irishness.
The Black and Tans burnt down the city centre of my home town, and shot a man on the first floor landing of my next door neighbours house, killed two unarmed civilians in my workplace, and ransacked the house I grew up in. The locations of B and T outrages were flagged up by an art project by a local artist in 2020. We’ve just had the decade of centenaries. Irish reunification is being discussed. The only member of the parachute regiment to stand trial for the murder of unarmed civilians on Bloody Sunday has not yet been tried. Forgive me for not thinking this is ‘old news’. Forgive me also for thinking that you might want to think a little harder about why people might be discussing outrages perpetrated by the British army upon innocent civilians, whether or not they fit your own narrative of what constitutes ‘current news’.
No one of any nationality should be bullied for their nationality. Why would someone like me think otherwise, when I had such unpleasant treatment at the hands of a minority of English people, often unexpected ones? But the OP chose to give no details about the circumstances in which ‘Come Out Ye Black and Tans’ was being sung in her workplace. If it was being done to intimidate her and make her uncomfortable, then of course that is completely unacceptable, just as the regular assumption that I must have approved of IRA bombings, or actually being a member of the IRA, was, or being pulled aside regularly in airports and ferry ports when travelling to and from England when I first started travelling there.