As has been posted elsewhere, predicating redundancy purely on performance (promotion boards or annual reports) is contrary to the spirit of UK employment law.
Nowadays all public sector employers (including the MOD) stick strictly to the laws and guidelines laid down in legislation.
I'm out now, so no longer current, but in the past when a redundancy tranche was announced, the criteria was detailed at the same time...usually with the caveat that voluntary quotas will be filled first.
Whilst the terms of redundancy may change, the process is unlikely to change......much.