Thank you for your inquiry. If the other doctor is employed by the partnership (as opposed to being a partner of the practice) then if you are to make him redundant you may have to pay him a redundancy payment if he meets the criteria laid down in statute. They same criteria would obviously apply to the doctor's wife.
The criteria to be eligible for a redundancy pay are:-
1) The person must be employed
2) The person must have been dismissed (ie. contract terminated by the partnership)
3) The person must have been continuously employed for at least two years
4) The person must be over the age of 20 at the date of dismissal
5) The person must have been dismissed by reason of redundancy.
In your case the particular type of redundancy is called "job redundancy".
Provided a person meets the above criteria they will be entitled to a statutory redundancy payment under s163 of Employment Rights Act 1996. This can be calculated easily by the following calculator: http://www.direct.gov.uk/redundancy.dsb
If either of the employees' contracts provide for a more generous redundancy payment then you would be bound by the term of the contract.
I note you say her performance has been poor. In other circumstances you may have been able to avoid making a redundancy payment by dismissing her on the ground of either capability or misconduct, however as an employer the practice would have had to have followed disciplinary and dismissal procedures in order avoid a claim for unfair dismissal. On the facts (ie. that the partnership would appear to be coming to an end at the end of the month) this would not appear to be an option for you.
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