1. Dear Paul, you are correct, that there will be clear issues as to the credibility of the Claimant claiming a larger amount today then he claimed when the Letter before Action was written. It will immediately raise the inference that one of the amounts claimed is wrong. In essence this weakens the Claimant's credibility and his case. However, the law does not prevent a Claimant from claiming a larger amount in his County Court proceedings that he claimed in his Letter before Action. So whilst the issue does to credibility, it is not fatal to the claim made.
2. Secondly, if you submit a defence, the case will proceed to hearing. The County Court will not make a judgment without hearing the actual evidence in the case, as it will be clear there is a dispute in issue which cannot be resolved without oral evidence. Additionally, there is the issue that the amounts claimed by the Claimant vary.
3. I regret to say you cannot claim for your time as a lay person in defending the claim. If you hire an expert you can claim for their time. Secondly, the claimant can withdraw his case. However, he will be left with a liability to you in costs. So, expect the Claimant to negotiate if he wishes to withdraw his claim.