1. By "housing executive" I take it you mean Housing Benefit, which is paid by the local authority. This is paid in arrears and not in advance (generally paid every 4 weeks).
2. Most tenancies say that rent is due monthly in advance, so effectively if most of your rent is paid by housing benefit you are always in rent arrears. Responsible landlords understand this and accept it - they know that the rent is more likely to be paid without problems if they are getting it (or most of it) from the local authority.
3. If you have a normal assured shorthold tenancy the landlord cannot evict you without a Court order. Any attempt to do so is illegal and a criminal offence.
4. Go to your local CAB for more detailed advice.