Why does my digital tv signal disappear during the day?

I moved house about a month ago from one side of Norwich to the other. We had perfect digital tv signal in our old property but now have very strange problems with the new property. Our TV uses an internal freeview signal tuner and we have an external aerial mounted on the roof. We get perfect signal for all channels in the morning (until about 8 am) and then the signal almost completely disappears and we only only get two channels (itv3 and bbc4) but with perfect picture. The channels then mysteriously reappear later at varying times usually between 6-9 pm and the quality of the picture gets progressively better as the the evening draws on. I have exhausted all possibilities within my knowledge to what the problem is. I have tried moving/repositioning the tv and have rewired the aerial adaptor and replaced the parts, I have also tried a signal booster but it just made things worse. I fanyone has any idea on this problem I would be a very happy man. Although the tv is awful during the day I would still like to receive a decent picture as I pay my tv licence! :(