The restriction on mortgage interest is the defining issue, and it has reshaped the arithmetic for leveraged landlords. Interest is no longer deducted from rental profit; instead you get a basic rate tax credit, which means higher rate taxpayers pay tax on rent they never really received. That pushed many landlords to consider holding property through a company, where interest remains deductible — but transferring existing property into a company is a sale at market value, triggering capital gains tax and stamp duty, so the arithmetic often fails for an existing portfolio while working for new purchases. Beyond structure: ownership shares between spouses, the timing of major works, replacement of domestic items relief, and keeping capital and revenue expenditure properly separated, which is where most landlord enquiries begin.