This is an aggressive debt worker trying to put the frighteners on you. As already said, they can't send bailiffs until they have a CCJ and you have defaulted on its terms. They may send a debt collector (but that is very unlikely). If they do, they have no powers or rights. Even if it gets to the stage where bailiffs might come, they cannot break into your property. They can only get in through an open door or window. You are entitled to deny them entry. But if you have a car they can clamp it and take it; also if you have unlocked garage/shed etc. they can take things in them. They can only take your possessions - not your partners. but sometimes they are not too careful about this and demand proof that the items do not belong to you.
If they do apply for a CCJ you will get a Court form to complete with details of your income & expenses. You must do this and send it to the Court by the deadline date, and make a realistic offer to pay by instalments (even if you only offer �1 per month). If the Court makes a decision you will not be able to keep to, you can apply to have it varied.
Creditors are sometimes more aggressive if they know you own a house, as they want to get the debt secured on the house by putting a charge on it (& possibly applying for an order for sale). They can only do this if you have defaulted on a CCJ.
This can all become quite complex, and you really need free independent advice - either from your local CAB or other debt advice agency, or from CCCS or National Debtline. Do not get involved with any outfits that charge fees.
What the creditor ought to accept in this sort of situation is an income & expenditure statement with an offer of monthly payments of the amount you can reasonably afford. The advice agency can help you with this. It is important that you take action on this now, and do not just leave it.