Hi - in Ontario (Canada) in present day, the brackets on a birth/marriage/death registration indicate information entered in error or information to be ignored. So, basically the brackets indicate (Ignore this). Somethin bracketed usually is followed by a correction. "(Niel) Neil" on my birth registration would indicate a missplelling (to be ignored) and the correction.
I do not know if it was the same in England in the 19th century.