The principle behind TOMS is that the tour operator buys the services (transport, hotel, meals, entertainment, etc.) that make up a tour from various suppliers, under various VAT regimes (UK or not, standard or zero rated or exempt, etc.) and, when charging their customer, pass on the gross cost (including whatever VAT had been paid, to whichever taxman), adding a margin (for their own costs and profit), together with VAT on that margin: roughly equating their tax treatment to someone assembling the tour themselves, or just for a friend.
What
The Guardian expected in March was that Uber Ltd (or whichever Uber Group company it was) would be assembling the taxi service they provide and supplying it, charging their costs (for car, fuel, driver's pay, etc.) and profit (like any normal supplier), together with 20% VAT on top.
Instead - based on what the receipt indicates - they are regarding the taxi trip as a 'designated travel service' (within the meaning of TOMS, i.e. as a 'tour'), charging the rider the gross cost they pay the actual taxi operator (which in many cases will be the driver), which pays for car, fuel, insurance, etc (including any VAT charged), together with their (Uber's) costs and profits (i.e. margin - which might be described as service fee), plus VAT on that... See also
https://help.uber.com/riders/articl...e?nodeId=2fedafb1-af1b-4bb1-b912-d55cd9861a13
Unfortunately part of Uber's business model is concealing who is actually providing what service to whom, and on what contractual basis...