There have been only about a dozen artists who have had posthumous UK number 1 hits. But one of those hits actually knocked another posthumous hit off the top spot - name either artist.
l'm afraid to guess since I live in the US, but here is a question about a US artist along the same lines.
One artist, the child of a another famous artist, remade their father's top hit song after his death, editing and remixing the original song to create a duet with both of them singing. The rearranged song won 3 Grammy Awards, including Best Song of the Year. Name both artists.