In the case of Mirab v Mentor Graphics the Employment Appeal Tribunal has set down some useful guidance for a redundancy process.
It first tackled the controversial issue of 'bumping'. Bumping is where a potentially redundant employee is moved into the job of someone else who is then made redundant instead of them. This is very often an impractical move but in many circumstances an employer should consider it. If there is any indication that a redundant employee might be interested in someone else's role, at least review the possibility of bumping. If it is discarded as an impractical option, make a note of this. There are no hard and fast rules, the question is whether the overall approach of the redundancy was reasonable.
Further, on the separate question of whether there are any vacancies so as to enable an offer of alternative employment, it is safest to alert a redundant senior employee to vacant junior roles and vice versa. You need not slot them in, just explain to them there will be an application process. The employee is unlikely to be interested, but they will not then be able to base a claim on a failure by the employer properly to consider alternative roles.
Finally, always have a right of appeal. Even if the redundancy process has been faultless up to the date of dismissal, a failure to allow an appeal, or a flawed appeal process, can then make the whole redundancy process unfair.
In summary, carefully consider, and be seen to consider, the circumstances of the redundant employee and the possibility of them being retained.