In 1907, the newly established Board of Education found that greater capacity for higher technical education was needed and a proposal to merge the City and Guilds College, the Royal School of Mines and the Royal College of Science was approved and passed, creating The Imperial College of Science and Technology as a constituent college of the University of London. Imperial's Royal Charter, granted by Edward VII, was officially signed on 8 July 1907. The main campus of Imperial College was constructed beside the buildings of the Imperial Institute in South Kensington.

Answer this question, if possible (if impossible, reply "unanswerable"): When was the charter signed for the University of London?
unanswerable