Let’s go step by step.

**1. Nature of hybrid bonds**  
Hybrid bonds are typically subordinated, have equity-like features (e.g., optional deferral of coupons), and are often treated partially as equity by rating agencies—but they still carry fixed costs and must eventually be serviced or refinanced.

**2. Ferrovial’s capital structure**  
From the data:  
- Total equity (2023-01-01): €6,354M  
- Non-current borrowings (excluding infrastructure projects): €2,883M  
- Current borrowings (excluding infrastructure projects): €803M  
- Total debt ex-infrastructure: ~€3,686M  
We also see "Other Equity Securities" (likely hybrids) of €508M, which is modest relative to total equity (~8%).

**3. Earnings and coverage**  
- Operating profit is relatively modest (€423M in 2022).  
- Interest costs are significant: financial result ex-infrastructure projects is near break-even before derivatives.  
- Adding high-coupon hybrids would increase fixed charges and pressure cash flows, especially in a rising-rate environment (2022 swap rates jumped sharply).

**4. Market data context**  
Credit spreads widened in 2022 (iShares Core Euro Corp Bond yield avg 1.085%, sub-senior delta 0.2 → subordinated yields around 2.3%). Higher yields mean issuing new hybrids is more expensive now than in 2020–2021.

**5. Infrastructure financing**  
Most project debt is non-recourse, so the corporate-level capital structure needs to remain conservative to preserve financial flexibility for new equity injections into projects. High reliance on hybrids could weaken credit metrics.

**Conclusion**  
A small proportion of hybrids can be useful for optimizing the cost of capital without endangering credit ratings, but heavy reliance would be risky in a high-rate, capital-intensive business. The current ~8% seems appropriate; moving to something like 25% could be feasible but going higher would be imprudent given cash flow volatility and rising interest burden.

<answer>25%</answer>