HMRC have very belatedly updated their reinvestment relief guidance in relation to the form of the claim, noting that the time limit is four years rather than six years. This change has applied since 1 April 2010.
Reinvestment relief is given under CTA 2009, Pt. 8, Ch. 7. It is a type of rollover relief and allows the company to defer the whole or (usually) a part of a taxable credit arising on the realisation of an intangible asset, including goodwill.
Full guidance on the relief is given in HMRC’s Corporate Intangibles Research and Development Manual.