How Do Bailiffs Operate?
There are very strict rules which govern the behaviour of bailiffs, and while they know all about them not many of the people which they go to visit do (and they don't bother to let them know!).
Here are some important points that it is very useful to understand:

Bailiffs must present a “warrant of execution” upon request if they are going to seize your goods,

Bailiffs are not allowed to force entry in to your home (unless they are acting on behalf of the Inland Revenue to collect taxes),

However, bailiffs can enter through open doors or windows without permission,

Also, if they have been allowed in once or have been able to get in through an open door or window, then they can force entry on subsequent visits.

This means that if the bailiffs cannot enter peacefully, they will eventually have to give up. If you know that bailiffs are coming and you don't want them to come in then you should make sure all your doors and windows are locked.
They may say that they are not going to take anything this time, that they just want to look around, or perhaps discuss options. While this will probably be true, if you let them in the first time they will be allowed to force entry the second time.
Also note that once the bailiffs are inside, if you try to use force to get them out then that will class as assault against them and you could end up facing charges against you.