Roymondo:
Contributing £100 a month isn’t really “taking it seriously” (unless you are a 20 year old on £10k a year). If you’ve been making contributions at that level for 40 years, it’ll maybe get you a few hundred pounds a month.
No idea what calculators you use but you may want to consider using a different one as yours is quite broken. £100 a month equivalent assuming annual 2.5% inflation and a return of 5% gives a retirement pot of £220k. You could draw down £8,800 a year minimum as a safe withdrawal rate and never touch that £220k principle sum. You could draw down £15k a year and it would most likely see you out.