HMRC have updated their guidance Changes and issues affecting the Corporation Tax online service.
Information about using box 773 for the 50% first-year allowance has been updated.
https://www.gov.uk/guidance/changes-and-issues-affecting-the-corporation-tax-online-service
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Capital Allowances, by Ray Chidell and Jake Iles, offers in-depth coverage of plant and machinery allowances, structures and buildings allowances, and all other UK capital allowances.
Full reference is made throughout to legislation, case law and HMRC guidance.