You can declare BR as many times as you like but depending upon why you were BR before and why you need to declare now you may have a BRU imposed, which would increase the period that the bankruptcy restrictions applied.
Remaining self employed shouldn't be a problem as quite a few people on this board have been self employed when declaring BR.
In this situation you would not get a BRO/BRU (at least not for going bankrupt twice). The reason being that only 2(or more) bankrupts within a 6 year period could result in a BRO/BRU. Additionally there was a change of legislation in 2004 which means that the one under the previous legislation would not count for these purposes