I can't tell you the U number for this. It is marked L. Y. R. 07. on one side and BULLERS, LTD. over LONDON on the other. The top is unglazed. There is a factory chip which was glazed over below the R.07 and the inner skirt is chipped away in two locations. Dated Lancaster and Yorkshire Railway insulators are, as I understand it, very difficult to find. $28.50 plus postage.