Right now, the full UK State Pension stands at £12,548 a year. That’s not a bad chunk of cash to boost your retirement living. But is it enough to support a comfortable lifestyle? Absolutely not.

What’s more, things could get a lot worse as the UK struggles to fund its booming elderly population. Investors who don’t take action today could be setting themselves up for a fall.

The problem

The Mercer CFA Institute Global Pension Index ranks the world’s State Pensions based on adequacy, sustainability and integrity. It’s the gold standard when it comes to evaluating different pension systems.

So what does it say about the UK? Well out of 52 countries, Britain’s pension system is ranked 12th. So it’s not terrible compared to many other countries. But then again, it’s not outstanding either.

For adequacy, the UK State Pension has just a B+ rating. Given the rising cost of living and social care, this doesn’t come as a surprise.

According to Pensions UK, the average single person requires £43,900 for a comfortable retirement. Stripping out the State Pension, that leaves £31,352 for retirees to make up.

Forget about luxuries like holidays abroad and giving cash gifts to loved ones. A shortfall of this size leaves millions of people in danger of paying for just the essentials.

Here’s what you could do

And things could get much worse for those retiring in the coming decades. Under the sustainability category, Mercer gives Britain’s State Pension a poor ranking of C+.

It’s time for Britons to take charge then. For those retiring 20-30 years from now, there’s still plenty of time to build a big nest egg for retirement.

Past performance isn’t a guarantee of future rewards, but the stock market has proven a reliable way to build long-term wealth for decades. Since the 1950s, share investing has delivered an average annual return of 9%.

It’s the sort of performance that can turn drip-fed investments into a formidable financial buffer. Let’s say you invest £500 a month in a tax-free Stocks and Shares ISA for 25 years. At the end of the period, you could have a portfolio worth £560,561, based on previous stock market performance.

A regular £39,239 income

If this was then invested in 7%-yielding dividend shares, you’d have an extra £39,239 in your hand every year. Dividends are never guaranteed, but a diversified portfolio of stocks can deliver a large and reliable second income.

So what shares should retirees consider for dividends? Aviva‘s (LSE:AV.) one of the best, in my view, which is why I’ve bought it for my own income portfolio.

Annual payouts here have risen for each of the last six years. The company’s undergone significant restructuring to support this, and is increasing its share of capital-light businesses to support dividends. By 2028, it hopes to generate 75% of earnings from capital-light businesses, generating formidable cash flows to fund future shareholder payouts.

The FTSE 100 firm faces competition risks across its operations. But I’m optimistic Aviva’s diverse mix of products, combined with its robust position in a growing sector, will deliver long-term passive income to supplement the State Pension.