Hi Jan and welcome to GoY. You don't say where you live in the UK which makes answering your question less easy. If you had the snow and long period of frost that many of us did last winter it is very likely that your magnolia is dead. We lost two this last winter as the sap was still up in the tree when the bad weather came.

And if you planted it since the winter, again, knowing where you are would have helped, because I don't know whether drought could be a possibility - certainly would be in the south, very difficult to keep any newly planted one damp enough at the roots. Where is it planted, what conditions I mean, sun/shade, damp soil, dry soil? Is your soil alkaline?