They have no right to come in, if they have not been into your home before to collect the debt, they cannot break in however you can choose not to let them in.
DON'T open the door to them as they may try to push past you. If they get inside, they may have a right to enter again and may break in to take your goods.
DON'T leave windows open or doors unlocked - bailiffs can legally get in through these. Bailiffs CANNOT get the police to help them break in.
BEWARE some bailiffs may leave you a phone number, and arrange to come round to 'have a chat'. Don't let them in, even if they say it's only to use the toilet or make a phone call.
Bailiffs MAY try to break into sheds, garages, greenhouses etc., even though this is illegal. KEEP VALUABLES SAFE! They may be able to take cars, motor-bikes and other vehicles parked near your home.
Politely but firmly refuse to let the bailiffs in. Offer what you can afford to pay. If the bailiffs accept your offer, ask them to return to their car, and go out and pay them. Make sure you get a receipt.
DON'T SIGN ANYTHING! If the bailiff leaves papers for you to sign and return, you do not have to do this. You don't have to sign agreements posted through your door either.