The bolt is considered a component part and as such is a prohibited part and must be listed on your FAC.
See this, chapter 13...............https://www.gov.uk/government/upload...35385/0088.pdf
Also from the CPS:
"component parts". R v Clarke (F), 82 Cr App R 308, CA states that the component part of a prohibited weapon is itself a prohibited weapon. Although there is no statutory definition, the Home Office Guidance to the Police at paragraph 13.70 states the following:
The term "component part" may be held to include (i) the barrel, chamber, cylinder, (ii) frame, body or receiver, (iii) breech, block, bolt or other mechanism for containing the charge at the rear of the chamber (iv), any other part of the firearm upon which the pressure caused by firing the weapon impinges directly. Magazines, sights and furniture are not considered component parts.