So according to some, Grecian Kebab is a tax evader.
Missing the point somewhat.
Taking cash makes it much easier to evade tax by not declaring income/turnover. It's as simple as putting some of the cash in your pocket rather than through the till.
Taking card payments means you generally have to employ an accountant to find more convoluted ways of evading tax as there's an audit trail for all of the income/turnover. This is where business ownersdo things like buying furniture/TVs/etc for their business but they end up in their own home.
I've had various chats with London cabbies over the years. Some of them are quite open about why they prefer to take cash, of the ones that did talk candidly to me the general consensus is that they put about 1/2 to 2/3 of their fares through the books (any less and it looks dodgy compared to the mileage/fuel they are claiming). The rest goes straight into their pocket as undeclared income (with no corporation tax or income tax to pay). It's got to the point that it is so rife there's no way it can really be tackled. (Obviously there will be some taxi drivers that do put everything through the books, they're not all crooks). (It's not limited to London taxi drivers, private hire drivers could do exactly the same thing.)
It's why the London Taxi Drivers Network (or whatever it is) are so against card payments (and why the card machine, if present, is so often "temporarily out of order") or smart Taximeters that track journeys, print receipts and (most importantly) are auditable. The usual deflection tactic is to point to Uber (the corporation) and say that they don't pay enough/any corporation tax - conveniently ignoring the fact that the individual Uber drivers can't easily avoid paying tax as they don't receive cash for fares and everything they earn is easily auditable.
It's not just cab drivers either. How many people have a cleaner and pay them in cash? Do you think all of that is being declared? Do you think waiting staff declare every single penny of their cash tips as they should? etc.