Oh dear.
I have had 20 years working in private sector. I have always saved the max possible into pensions from when I was allowed to do so, up to 8% of my salary plus any employer contributions. I have approx £200k saved into a private pension.
(Note, current value of money assumed at all times below).
3 years ago I went into local government. I pay 9.9% of my salary into the pension. After 3 years I have paid approx £27k of my own money in. I have a guaranteed final salary pension of £5500 p.a.
If I were to buy an annuity on the open market today for £5500, I would be looking to spend approx £125k. I have actually spent £27k to get to this amount. This is only over 3 years. If I were to stay for 20 years (!), I would contribute £180k but get a pension of £43k. To buy £43k on the open market via annuity would cost just under £1m.
When I joined, I was given the option to transfer in my private pension into the LGPS. I chose not to, as I was well aware that I could only take the LGPS from state pension age, and I might need my private pension to tide me over until then, if I wanted to take early retirement.
All of this is clear when you look at joining the LGPS.
Anyone who doesn't join the LGPS when offered the chance is stupid. And doesn't understand the reality of pensions. No amount of saving into an ISA or whatever can make up that sort of difference.