There are three UK R&D Tax Credits regimes that companies can claim under. Which regime (or combination of regimes) will be claimed depends upon the size, revenue and assets of the company as well as the nature and accounting treatment of the R&D costs.
Three Tax Regimes
SME (Small and Medium Enterprises) Regime: Available to companies who meet the SME size requirements, the SME regime is generally the most rewarding of the three regimes. As well as meeting the size requirements, qualifying companies also need to be undertaking R&D projects that are revenue in nature for tax purposes.
RDEC (Research and Development Expenditure Credit) Regime: The RDEC regime is for large companies that are undertaking R&D that is revenue in nature. RDEC provides an 11% 'above the line' credit.