No you do not have to do this. It's completely up to you.
The Office of National Statistics does collect information in this sway , but it is entirely voluntary. They will give you a small gift voucher (about £10) for helping them out.
If you give them a call and say that you do not want to participate, they won't come.
The actual interview involves asking you about your income, your health, what government services you use etc. It is quite detailed and is a lot more comprehensive than the census information. But you do not have to do participate.