What are the differences in claiming as an SME or under RDEC as a large company?

While there are differences in rates, the main difference between claiming as an SME versus under RDEC is the accountancy treatment. 

For SMEs the tax credits are non taxable, and will only affect your tax liability. Under RDEC, the R&D credits that companies receive under RDEC are classed as credits when calculating the pre-tax profit.

Simply put, the SME scheme is what’s known as a below the line benefit, while the RDEC scheme is an above the line benefit.