If there was a problem with your husbands timekeeping then they should have given first verbal warnings, then a written warning. Presumably they have evidence of your husband not keeping to times. You could try getting in touch with ACAS, they might be able to give you advice. Suddenly changing from nights to a day shift might be very inconvenient and not sure what could happen if your husband refused.

http://www.acas.org.uk/index.aspx?articleid=1461