Hello,
Technically, M. major is only frost hardy, just below 0°C, so long as
wood has been summer ripened.
Suggested to protect from winter cold and wet.
THe growth affected by the frost will die back, but as this is a
pruning group 7 (down to the ground) plant, so long as its roots
servive the winter you should be OK.
Good luck

Clifford
Doncaster