Top 50 Insurers 2026: What size really says about underwriting performance

This year’s Top 50 Insurers report once again features the largest 50 insurance groups across the UK and Gibraltar, which control more than £95bn of gross written premium (GWP) and span a wide range of business models and specialisms.

But what role does size play in delivering profitable underwriting results? And does a bigger premium base necessarily mean stronger ratios and financial performance?

To help answer these questions, market intelligence firm and Top 50 Insurers data provider Insurance DataLab (IDL) analysed the underwriting results of the non-Lloyd’s insurers included in 2026’s ranking and compared these with underwriting performance across the rest of the UK general insurance (UKGI) market.

Based on each insurer’s latest Solvency and Financial Condition Report (SFCR), IDL’s analysis found that the 2026 cohort of the Top 50 Insurers reported an aggregate combined operating ratio (COR) of 94%. This is some 4.5 percentage points ahead of the 98.5% aggregate COR reported for 2025/26 across those insurers that did not make this year’s ranking.

The main driver of this difference in performance can be found by looking at the expense base of these two groups. Indeed, insurers within the Top 50 Insurers list this year reported an aggregate expense ratio of 31.5%, compared with 37.7% for the rest of the market.

This 6.2 percentage point advantage more than offsets a weaker claims performance for the larger insurers. The Top 50 Insurers 2026 cohort recorded a loss ratio of 62.5%, according to their most recent SFCRs, while their smaller peers achieved 60.8% – a difference of just 1.7 percentage points.

These figures are consistent with the economies of scale explored in last year’s report.

A larger premium base can support shared systems and centralised operations, allowing insurers to spread costs across a broader book of business.

Smaller insurers, meanwhile, continue to demonstrate the potential benefits of specialisation. Their lower aggregate loss ratio is consistent with the benefits of a more focused portfolio and specialist risk selection, even where they lack the scale to match larger competitors on expenses.

The latest results also show that this balance is changing, however, with both groups improving their underwriting performance over the past year – albeit in different ways.

For the Top 50 Insurers demographic featured in this analysis, the latest COR result represents a 2.2 percentage point improvement on the 96.2% reported for 2024/25.

This improvement was driven by claims, with the aggregate loss ratio falling by 2.5 percentage points. The expense ratio moved in the opposite direction, increasing by 0.3 percentage points and offsetting part of that gain.

This pattern was more pronounced for insurers outside the Top 50 Insurers list, which reported a 6.5 percentage point reduction in their loss ratio for 2025/26 compared to the previous year – although much of this was offset by a 4.5 percentage point increase in the expense ratio.

Despite this improvement in the loss ratio, the figures also highlight one of the downsides of a smaller and more focused book of business – volatility. Particularly when it comes to the loss ratio.

Indeed, over the last three years, insurers outside the Top 50 Insurers cohort reported volatility of 4.2 percentage points – almost double the 2.3 percentage point volatility recorded by larger insurers that were included this year’s ranking.

Top 50 cohort under the microscope

The relationship between scale and performance becomes more varied when analysing the premium bands of this year’s featured firms.

The largest 10 groups in 2026’s Top 50 Insurers research reported an aggregate COR of 94.8%, with a relatively low expense ratio of 29.7%.

The story is different, however, when exploring the claims picture, with these largest insurance groups reporting a loss ratio of 65.1% – the second highest of all the premium bands in this analysis.

Although all five premium bands dissected by IDL reported an underwriting profit, the top 10 insurers had the highest aggregate COR of 94.8%. Their result was also 0.8 percentage points above the aggregate position across the entire Top 50 Insurers cohort.

The strongest performance came from insurers in groups ranked 21 to 30 in the Top 50 Insurers 2026, with this demographic achieving an aggregate COR of 84.3%.

This was underpinned by a loss ratio of just 40.3%, comfortably the lowest across the five premium bands – this claims performance was strong enough to accommodate an expense ratio of 44.1%, the highest in this analysis.

It is worth noting, however, that many of the insurers ranked between 21 and 30 in this year’s report are specialist commercial lines insurers handling complex specialist risks. This business mix can contribute to higher expense ratios and greater year-on-year claims volatility.

For example, insurers ranked between 21 and 30 this year reported loss ratio volatility of five percentage points – more than double the 2.3 percentage points reported for the entire 2026 cohort of Top 50 Insurers and also greater than the 4.2 percentage point volatility reported for insurers outside of this year’s ranking.

Meanwhile, those ranked 11 to 20 in 2026’s list reported an aggregate COR of 93%, while insurers in groups placed 31 to 40 achieved 93.7%. The latter cohort also combined a relatively low loss ratio of 50.8% with a higher expense ratio of 42.9%.

At the other end of the cost comparison, insurers in groups ranked 41 to 50 recorded the lowest expense ratio at 27.5%. However, their loss ratio of 66.7% was the highest of the five premium bands, leaving an aggregate COR of 94.2%.

Throwing the cat among the pigeons, the performance results for insurance groups ranked 41 to 50 are skewed by one insurer reporting negative expenses as a result of reinsurance commissions that more than offset its acquisition costs, which has materially lowered the aggregate expense ratio for the cohort.

When this insurer is excluded, the expense ratio rises to 29.8% and the COR to 97.1%.

Sustaining underwriting returns

These results show why an insurer’s position in the GWP ranking provides only part of the explanation for its profitability. The balance between claims and expenses varies considerably, even among the largest insurance groups in UKGI.

For the largest insurers, the latest results point to the importance of improving claims performance while preserving the cost advantages that come with scale. The top 10 already operate with a relatively low expense ratio, yet other sized premium bands are achieving stronger underwriting margins.

For smaller insurers, the challenge is to retain more of the benefit from improving loss ratios. On the comparable sample, rising expense ratios absorbed more than two-thirds of the improvement in claims performance over the past year.

A growing premium base can help spread those costs, but the results for insurers ranked 21 to 30 show how strong loss ratio performance can outweigh a higher cost base. Sustainable profitability depends on keeping both sides of the COR under control as the business develops.