No, you don’t need to put down a deposit when remortgaging. You can use equity you have in your home as a deposit.
Equity is the cash difference between how much your home is worth, and how much you have left to pay on your mortgage. Let's say you sold your house for £500,000 with £300,000 still left to pay on your mortgage. Your equity would be £200,000. You won't have equity from an interest-only mortgage unless your house has gone up in value.
However, if you’re looking to significantly reduce your monthly repayments and get the very best rates, putting down an additional deposit may be an option. Doing this lowers your LTV (the size of the loan compared to the value of the property), giving you access to the better deals. A professional mortgage broker can help you to understand your options.