This may depend on the reason for the enforcement. If it is a straightforward case of a civil debt then they cannot do anything so long as they cannot get into your property (i.e. your own flat - them getting into some other part of the building doesn't count). There are some types of case (Court fines etc.) where they may be able to force entry. There is a website (I think it is bailiffsonline.co.uk) with quite a bit of info. - look it up.
If they do come when you are in make sure you don't let them into your flat unless you are absolutely certain that otherwise they would have the power to force entry (& don't make that decision based on what they tell you - it may well be an inaccurate statement).
Do note that if you leave any of your property in the open (e.g. a car) they can "take" that - normally by clamping it.
This problem is not going to go away, so make arrangements as rapidly as you can to pay off the debt by coming to an agreement to do so by instalments - but make sure they are payments you know you can afford as you must not fail to make them.