All the FTSE 100 banks have been falling lately, but Barclays (LSE: BARC) shares have fallen fastest, down almost 25% in three months.

Over the same period, Lloyds and HSBC both fell around 12%, and NatWest by 8%. Wider economic and geopolitical uncertainty has rattled investors, particularly fears that rising inflation will push interest rates higher and squeeze borrowers.

Higher rates can help banks widen their net interest margins, but that could be offset by slower growth, weaker demand and rising bad debts.

The banks had to retreat at some point. They’ve had a terrific run over the past three years. So is this a buying opportunity, particularly for Barclays?

The cheapest bank in the world?

Analysts have dubbed Barclays the “cheapest bank in the world”, trading at a discount to its European rivals. Its price-to-book ratio is now just 0.71, depending on the source, meaning it trades below the accounting value of its net assets.

By comparison, HSBC trades at around 1.6 times book value, Lloyds at 1.3 and NatWest at 1.2. Barclays often trades at a discount because investment banking brings greater earnings volatility, but the gap is striking.

Today, investment banking looks riskier amid uncertainty over the global economy and the sustainability of the AI boom. Yet Barclays is working hard to drive profits, announcing plans to cut around 5,000 jobs as it uses technology and AI to improve efficiency. Grim news for employees, though.

Latest results disappoint

Third-quarter results (22 October) were mixed. Pre-tax profit rose 12% to £2.3bn, but missed forecasts of £2.4bn. Total income increased 3% to £7.4billion, also below expectations.

The investment bank was the main disappointment as fixed-income, currencies and commodities revenue dropped. Lower client activity in rates and credit, particularly towards the end of the quarter, outweighed a 47% jump in equities trading income.

The board still announced a £500m share buyback, taking year-to-date shareholder distributions to £2.8bn, up 46% on last year. The trailing yield is a modest 2%. Under pressure chief executive C.S. Venkatakrishnan said he “would not be human” if he was happy with today’s share price, but reaffirmed the bank’s 2026 and 2028 targets.

Is the FTSE 100 bank worth considering?

Barclays’ price-to-earnings ratio is down to 9.3, compared with 15 for HSBC and Lloyds. Takeover speculation has also emerged, with reports suggesting a big player like JP Morgan Chase might find the valuation tempting.

I never buy on takeover rumours, but I am intrigued by how cheap Barclays looks. In fact, the only thing stopping me buying it today is that I already own HSBC, Lloyds and NatWest, and need to be wary of overloading my portfolio with banks.

We also need to see what Chancellor John Healey does in his Budget on Wednesday (28 October), with a possible hike to the bank windfall tax. Plus its volatile investment banking arm needs watching. With a long-term view, I think Barclays is well worth considering at this price, but investors should expect a bumpy ride.

There’s another FTSE 100 growth stock that’s suddenly cheaper than it was and may also be worth a closer look…

What growth stock do we like better than Barclays Plc right now?

One of our Share Advisor analysts has just released a brand new stock report that we think is a must-read for any investor looking to try and generate potential growth.

And the best bit is that you can see it for yourself, right now, absolutely free of charge!

No jargon. No hard sell. Just a clear look at a growth share idea we think is worth your time.

Harvey Jones owns shares in HSBC, Lloyds and NatWest.