One of the drawbacks of being a saver, that is, in cash, is that the needs of the economy and government are often against you. You will only receive a decent nominal return on your money (i.e. a high interest rate) when inflation has eroded your savings. And, given that policy makers seem to have a tendency to allow for higher inflation than they officially target, the odds seem stacked against you.

Recent periods of genuine deflation have been thin on the ground in the UK so most of the inflation errors have been in exceeding target. This means that for much of the time, the interest rate must have been too low and, therefore, the rates paid to depositors fail to compensate adequately.
 
Savers find it almost impossible to gauge the damage done by inflation, focussing solely on the nominal value of their funds so they tend not to be too bothered by this lack of compensation.
 
So, if you are a sever receiving 3% on your deposit (now that rates have fallen) and you pay high rate tax, you will receive 1.8% per annum on your money. Given that RPI is currently more than 5%, your money is losing more than 3% every year in real terms. Extend that over a long period and your wealth has been seriously damaged.
 

Of course, part of the justification for reducing rates is that inflation expectations have been reduced so, in time, the return gap should be reduced. The only problem is that if inflation does decrease considerably, rates may well come down again, compounding your misfortune. It may even out over time but the experience of the Seventies shows that it can take a very long time indeed, more than twenty years for cash then.

However, if you can take a twenty year perspective, you might be better off considering shares.