Will the claim be settled via an ACAS conciliation officer or a compromise agreement? ACAS may help if a claim has already been brought in an employment tribunal.
If a compromise agreement is to be used, have full factual as well as legal details of the claim being settled and all other potential claims been set out clearly?
Do you understand the very strict requirements necessary for the agreement to be enforceable and to compromise all of the claims you want? Careful drafting is required and a good up-to-date precedent should be used. Take legal advice.
If you are terminating and paying in lieu of notice, is there a clause in the employment contract allowing this? If not, the termination and payment in lieu will be in breach of contract.