Can I claim against a former employer who only towards the end of my employment introduced personal protective equipment in the form of ear defenders?

Yes. If there was no protection at all afforded until the introduction of ear protection, then you will still be compensated but the amount of the money recovered may be less than if there was no ear protection. Remember even though your former employer may have provided ear protection, it must be sufficient and do the job They may not be fitted correctly or totally inappropriate. If they provide ear plugs or cotton wool these barriers are unlikely to offer any protection .