Any business expense which is ""exclusively for the purposes of the trade" can be use to reduce a self-employed person's tax bill. (As he/she won't pay tax on the money used to fund that expense, it effectively means that they get 20% back if they're a Standard Rate tax payer). Nothing has changed; HMRC has simply reiterated the rule that has existed for decades anyway.
However do small businesses have seperate vehicles for work and other ? Complicates things,and may not help. Best scrap these highway robbery schemes, and the horse's rectums that are responsible for their creation.