These Regulations amend the Corporation Tax (Instalment Payments) Regulations 1998 (S.I. 1998/3175) which make provision for quarterly instalment payments of corporation tax by large companies. The Regulations have effect in relation to accounting periods of companies ending on or after 1st July 2005 and provide that corporation tax and the supplementary charge in relation to ring fence profits and adjusted ring fence profits (which arise from a company’s oil extraction activities or from oil rights) are payable in up to three instalments rather than four.