With my example your procurement team would also be acting to keep their customer.
This is the problem with SOME aspects of employment law. It can be very difficult to get rid of underperforming staff.
It's really not if you have the process in place to manage performance.
You need to set clear and defined performance levels, then help people to achieve them. Have action plans in place and regular sit downs.
If performance slips, find out why and try to rectify. Train find out why the issues are occurring etc and try to solve.
Make sure it's all documented and fair, and actually try to help them get to the standard. Then if they are still under performing, then you can formalise the dis apiary route.
It's not that hard, but it sounds like you are approaching the situation looking to sack and not solve a problem.