You would have to convert to a JAR PPL. Don't know about the IMC.
The other question is maintenance. I looked at running a D reg aircraft here recently and it looked as if it would have to go back regularly to Germany at least for its 3 year CofA. In theory it can all be done here by a JAR 145 maintenance org, but there's a big difference between theory and practice. I talked to Leon Winnert at the CAA in Gatwick about it. He was most helpful.
QDM