Housing Bubble 2: Return of the Ugly

Do you have a source for that £17k becoming over £28M?

This one looks simple enough, but I assume most use the same historical price index. I just used the annualized dividend-reinvested returns between the two dates: 10.913%

Incidentally, you can use that % to get a feel for how interest compounds. On a calculator, input 17 x 1.10913 then press = for each year since 1970 (usually just repeats last step). At first it will appear nearly constant, but note how the annual returns accelerate over time, especially as you approach recent years.

I currently have a pension pot worth about £70k and it's only forecast to be worth about £500k in thirty years time (when I would retire), and that is including my ongoing contributions.

You may want to check what funds they put you in by default. Often the default allocation is a “target-date” fund, which is an actively-managed (insidiously expensive) fund that begins with a modest volatility asset distribution and periodically redistributes for lower volatility as the target date approaches.

IME these funds invariably suck, mostly due to exorbitant fees but also because they are actively managed. It’s rare for any actively managed fund to consistently beat the market overall or as represented by benchmark indexes. (That may seem counterintuitive but the reason is “market efficiency.”) The only reason for active managed funds IMO is if you need moderate chance of gain paired with minimal chance of loss, which only applies closer to distribution.

If there's another way to invest that to make myself a multimillionaire in retirement, it'd be a no brainer.

With a 30 year timeline, volatility is your friend for quite some time. The simplest way to capture whole-market volatility is to just buy ETF shares tracking either Total Market Index or a benchmark index like S&P500. Most of these ETFs have very low fees. This “naive method” is very difficult to beat. Just make sure dividends are reinvested (usually a checkbox) so you don’t come back later to a pile of cash that hasn’t been working for you.

Then comes the most important step: nothing. Don’t mess with it. Buy and hold. Set and forget. Fucking with it (trying to time the market, panic selling, etc) is basically the only mistake you can make. Avoid that and you can rely on statistical probability.

I used the below link and assumed an investment of 17k in 1970 (that's assuming you have the cash to buy out right, rather than starting to pay a mortgage) and it only came up in the low six figures.

It looks like their figure is inflation-adjusted and assumes dividends are not reinvested. The former can be useful if you want to know comparable value. The latter isn’t, because you should always reinvest dividends. (Also it affects the S&P500 especially since that’s a large cap value index where much of the returns are actual dividends instead of just growth of the stock price.)