Just placing an advert promoting your services doesn't mean you are self employed from that point on. If you have made no sales, then there are no costs you can offset against it under historical cost accounting conventions. therefore by definition, you have not "traded" and have nothing to declare to HM revenue and Customs.
Contacted tax office in november and they said for registering purposes i had to give date of first advert placed in paper which was august .Just recvd bill yesterday for ni contributions for 52.00 for 6 mths so not too bad. Tax office advised wouldnt need to sort tax till next year as only been trading 6 mths.