In the UK, most lenders offer secured debentures; finding an unsecured one is pretty unusual.
A secured debenture means the lender’s investment is protected - there’s less risk for them in these instances. If you fail to repay, they can just claim against your assets, and if you’ve got a fixed charge secured debenture, and you need to sell assets to pay debts, you’ll first need to pay the lender or receive permission from the lender to sell.
With an unsecured debenture, a lender would simply wait their turn amongst other creditors to be paid - they don’t jump the queue.