A number of changes have been made to the Small and Medium Companies (SME) R&D and VRR tax relief schemes effective from 1 August 2008. For more information, see here
HMRC recently published a Brief announcing a change of HMRC interpretation which will apply where a company's SME status alters on or after 1 December 2008 for example, as a result of acquisition by a Large company. This will affect which R&D scheme such a company can claim under at various times. For more information see here