He may well lose his job but he did offer to resign, what happens as far as the benefits service are concerned? and of course future employers? not that they will be clambering over themselves with job offers.
Is he going to be sacked due to not being up to the job, or be made redundant because there isn't enough work to justify employing him? Or does he feel he has to resign because the workplace isn't safe, or it is affecting his health? It makes a big difference as to his status when he signs on.
If he resigns, unless for good reason as determined by the Unemployment Office, he will have made himself unemployed on purpose and will not be eligible for unemployment benefits for up to 26 weeks. Whereas if he is made redundant or has good cause to resign, then he will be eligible.