Genuinely self-employed people can claim travel and expenses related to their business. Employed people who permanently work a fixed place of work, cannot claim travel and related expenses. Contracting, however, was blurring the lines - until 2016.
From 2016, the government tightened legislation so that unless it can be proven that the contractor has full autonomy of the work they are undertaking, then expense claims for travel and subsistence would be disallowed.
Prior to the 2015 UK Budget, contracts using umbrella companies were making claims for travel and lunch etc for each contracting job they undertook. The same applied for directors of PSCs who would make claims for these types of expenses.
The Supervison, Director and Control test was put in place to put the onus on the claiming individual to prove the level of autonomy they have in the role - to essentially show that they could be deemed truly 'self employed' rather than 'employed' - and thus enjoy the benefits of claiming the 'business' expenses.