Bristow & Sutor have no right to force entry. They don't have any legal powers to do so.

Do I have to let Bristow and Sutor in?

Bristow & Sutor must usually give you at least 7 days' notice of their first visit. This is called the compliance stage. Bristow & Sutor cannot enter your home: by force, for example by barging past you when you answer the door.

Are debt collectors allowed to force entry?

They aren't allowed to force their way into your home and they can't bring a locksmith to help them get in. They'll normally leave if you refuse to let them in - but they'll be back if you don't arrange to pay your debt. It's important to do this as quickly as you can, otherwise the bailiffs can add fees to your debt.