Building a passive income portfolio in the UK doesn’t just take a lot of patience and dedication (although they assist). A portfolio made of law is equally critical FTSE100 shares.

But what are the “right” stocks?

Well, to be sincere, there is no definitive list of suitable stocks for such a venture. It doesn’t assist that the goalposts are constantly changing. Fluctuating interest rates, political instability and foreign tariffs all contribute to daily stock price fluctuations.

Therefore, the ideal stocks are those that remain stable even in tough times. If your investment horizon is 10 to 20 years (and it should be), you need stocks that can survive that journey.

With this in mind, I’ve identified two dividend stocks in the FTSE 100 that have an exceptionally reliable track record. Whether you’re preparing for retirement or saving for a home, I think it’s worth considering both.

Unilever

Despite typically moderate performance, Unilever (LSE: ULVR) is a popular source of passive income due to its exceptional dividend history. It has been operating for almost a century and has paid consistent dividends since 1929, with almost 20 years of uninterrupted growth prior to Covid-19.

That alone is impressive, but the real attraction is its resilience to market downturns. Even during the most severe economic downturns (the Great Depression, World War II, the 2008 financial crisis and Covid), Unilever maintained its dividend payments.

The reason is the company’s recession-proof business model. Selling crucial goods such as food, personal care and household products means revenue flows regardless of economic conditions.

It is worth noting that there is a risk of unexpected currency fluctuations affecting dividend payments as Unilever reports in both sterling and euro. Moreover, global diversification means that returns are at risk from political instability, currency crises and economic volatility.

However, history has shown that it is one of the most stable dividend stocks in the FTSE 100 index.

Severn Trent

When thinking about good utility resources that provide income, many people turn to them National Network. But while the main operator of the national grid is a great option, Severn Trent (LSE:SVT) actually has a better dividend record.

What’s more, it has performed slightly better over the last 20 years.

Like National Grid, Severn Trent is a regulated utility company serving around 4.7 million homes and businesses in the Midlands and Wales. As a regulated monopoly, the company benefits from predictable, inflation-linked revenue streams with minimal competition.

Although this is not a result close to Unilever’s record, it is doing surprisingly well in its 20-year history. Despite two petite dividend cuts over the last 20 years, overall dividends have grown at an average rate of 3.53% per year. For example, the company increased its dividend from 81p in 2016 to £1.19 in 2024, an raise of around 47% over eight years.

Another advantage of the regulation is the addition of provisions regarding inflation indexation, ensuring that dividend payments keep pace with rising costs. The crucial need for water means that incomes remain stable regardless of economic conditions.

But there is one elephant in the room that cannot be ignored: the £8.65 billion debt. At this level, even a regulated company is at risk of insolvency or at least a reduction in dividends.

However, from a long-term perspective, I expect debt to remain under control and the company to continue to provide stable earnings to shareholders.