Can I reuse a previous R&D tax credit claim?

No. If you have previously submitted an R&D claim, then you will not be able to resubmit a claim for a new case. However, HMRC do accept that R&D projects, especially the more complex ones, can last multiple years. In that case, it is important to detail the different stages of the project and the different spend for each year so while the project might be the same, the content of the documents will reflect the different stages and spend for each year. If this is the case, then you might refer to your previous claim to ensure there is no overlap and as a way of remembering where the project was up to at the previous year end.