If I had put 500 pounds sterling in a First Reserve Account with NatWest Bank in August 1990 about how much money would I have now if I hadn't touched it?
It's impossible to answer this question without access to records of the interest rates paid by NatWest over the past 18 years. However, based upon the current AER of 1.55%, you'd have �659.49.
However, that account was paying 1.80% AER back in March of this year. If that rate had prevailed throughout the 18 year period, you now have �689.33.