If your landlord or estate agent requires you to provide a guarantor but you do not have one, then there are some options.
If you can afford to then you could offer to pay some of your rent up front to the landlord, not all landlords may accept this but you could open a discussion with them to see if there is an agreement you can reach.
You could also consider using an external guarantor service such as Housing Hand and Rent Guarantor, however please be aware that using these services can incur additional cost to you, and remember to read through any contract you sign with them carefully.