The questions that come up most, in the order they come up.

A lender starts from a multiple of verified income and then applies an affordability assessment that can reduce it — deducting credit commitments and an allowance for household spending, and testing the payment at a rate higher than the one you would pay. Because lenders treat bonus, overtime, commission, benefits and childcare differently, the maximum varies between them on identical figures, sometimes substantially.

Most lenders want at least five per cent of the purchase price, with a limited range of products at that level. Ten per cent opens up materially more choice, with further improvements at fifteen and twenty-five. Pricing works in bands, so it is always worth checking where the next threshold sits.

It costs nothing and estate agents in most markets expect one before putting an offer to a seller. Its more useful function is diagnostic — if there is something on your credit file you were not aware of, this is when you want to find it.

An initial conversation and an agreement in principle normally involve only a soft credit search, which you can see but other lenders cannot, and which does not affect your score. Only a full application involves a hard search.

Register on the electoral roll, check your credit file at more than one agency, keep credit balances well below their limits, avoid taking on new borrowing, and gather your income and deposit evidence. If you can clear a small credit commitment, do — it often frees up more borrowing capacity than the balance itself was worth.

Several months before the initial period ends. Lenders will usually let you reserve a new rate that far ahead and hold it until the switch date, so starting early costs nothing and protects you against the case taking longer than expected. Doing nothing means reverting to the standard variable rate.

Almost always, up to an annual allowance expressed as a percentage of the balance, without triggering the early repayment charge. Overpayments reduce interest for the whole remaining term, so early ones are worth considerably more than later ones. Check whether your lender applies them immediately or only at the anniversary.

Contact your lender early — before a payment is missed rather than after. Lenders are required to treat customers in financial difficulty fairly and have a range of options available, and the earlier the conversation happens the more of them remain open. Free, independent debt advice is available and is worth taking.

Some lenders offer payment deferrals in defined circumstances, usually where the account is up to date and you have built up overpayments. It is not a right and it is not free — interest continues to accrue on the unpaid amount. Ask your lender what it actually offers rather than assuming.

You either port the product to the new property, redeem the loan and take a new one, or keep it and let the property with the lender's consent. Which is best depends on whether an early repayment charge applies, whether you are borrowing more, and whether the lender will accept the new property.