As things stand, I have 12 holdings from the FTSE 100 in my Stocks and Shares ISA. Some of these I’ve held for years, while a couple are newer positions initiated this year.

In no particular order, they are HSBC, AstraZeneca, Games Workshop, 3i Group, Scottish Mortgage, BAE Systems, Aviva, Legal & General, Sage (new holding), LondonMetric Property (new holding), and Coca-Cola HBC.

As we can see, this is a quite a motley group that spans various sectors. I hold Scottish Mortgage for growth, Legal & General and LondonMetric purely for dividends, and Games Workshop for both.

However, eagle-eyed readers will have spotted that I only mentioned 11 share above. So, what is the missing one?

Single stock, reveal yourself!

The biggest holding in my ISA today is Rolls-Royce (LSE:RR). Since Tufan Erginbilgiç took over at the start of 2023, the engine maker’s share price has gone parabolic. Happy days.

Now, I should point out that Scottish Mortgage, Games Workshop, and Wise (listed in London but not in the FTSE 100) are larger overall holdings because they’re also in my SIPP portfolio. And I have larger US holdings, including Axon Enterprise and Shopify.

However, Rolls-Royce has been an incredible performer since I initiated a starter position in mid-2023. I also topped up twice on dips in 2024 and 2025.

For the record, I had no idea the stock would skyrocket as quickly as it has (nobody really did). But it’s bittersweet because I did have an inkling this could be a big winner over time.

In March 2023, for example, I wrote that I thought we “could be in the foothills of a massive multi-year turnaround in the [Rolls-Royce] share price“.

So, why didn’t I invest more money (even if I had to trim or sell other holdings to do so)? This is the question I keep asking myself.

Of course, I’m speaking with the benefit of hindsight here. Back in 2023, I would have been delighted to see Rolls-Royce hit £12.50 per share by 2030 — it’s already there years ahead of schedule!

Attractive optionality

Looking ahead, I’m still bullish on the company’s future. It has multiple avenues for growth (optionality), from expanding in defence to selling and servicing many more passenger jet engines and supplying products for data centre backup power.  

Then there are small modular reactors (SMRs), which can be factory-built and deployed at far lower cost than traditional nuclear plants. Earlier this week, Rolls signed a contract with Great British Energy to get cracking on three SMRs for Wylfa, in North Wales.

This brings certainty to the UK SMR programme and differentiates our business as the only SMR company with multiple commitments in Europe — an initial three units at Wylfa and up to six units in Czechia.
Chris Cholerton, Rolls-Royce SMR Chief Executive

However, I’m also mindful that the stock’s trading at a sky-scraping 32 times forward earnings. At this valuation, any unexpected slowdown in growth could spark a sell-off. And the Middle East war adds supply chain risk moving forward.

Over the next decade though, I think surging travel demand, the AI infrastructure buildout, rising defence spend, and SMRs will remain four powerful investing themes.

Therefore, I’m more than happy to keep Rolls-Royce in my Stocks and Shares ISA.