Putting an existing portfolio into a limited company is not a tax formality. It is a commercial decision about reinvestment, cash you need personally, borrowing terms, risk, administration and your eventual exit. A company can be compelling where profits are retained for growth, but the headline corporation-tax rate is not a personal cash rate.
Moving property already owned personally is usually treated as a market-value disposal and acquisition. If s162 Incorporation Relief or Schedule 15 Partnership Relief does not apply, market-value CGT and SDLT can make the move uneconomic before any annual saving is realised. Model the transfer cost and the ongoing position together.
A company is often worth modelling for a higher-rate landlord with meaningful borrowing who plans to reinvest surplus rent. Companies normally deduct qualifying finance costs in calculating taxable profits, unlike an unincorporated residential landlord affected by Section 24. Corporation tax depends on profits and circumstances, currently with rates from 19% to 25% and marginal relief between thresholds.
That does not make incorporation universally better. If all rental profit is needed for living costs, salary or dividend extraction can produce a further personal tax charge; company ownership can be no better or worse after extraction tax. Compare actual lender terms, compliance costs, transfer taxes and the cash left to the owner, not just tax on retained company profit.