notanotheroneagain We can all read dogwhistles from play of words, Compton, mutt, comparing her to a pig (her oar in), play on words (niggling a play on the n word).
Honestly, this is really offensive and verging on racism itself. You have already had to have it explained to you that "niggling" and its derivatives are long standing words in English, because English is part derived from Old Norse. The original word is hnøggr, in which the initial "n" isn't pronounced and the ø is between an o and an i. Its spawned many derivatives across Norway Sweden, Scotland, northern England, etc all of which are based on its original meaning of stingy.
Not everyone in Britain is English or from London. The UK is a long island from north to south and many people speak dialects that are still rooted heavily in Old Norse, and "niggling" is a word which is commonplace amongst much of western Europe.
Considering that in the UK and the EU, you can discriminate on grounds of nationality, it is your remarks which are potentially racist, not the use of a word which has been in the English language for centuries.
Its really easy to google, which might be more appropriate than accusing people of being racist when using their own language in a perfectly normal way.