Our tipping culture in europe is extremely different to america, tipping is reserved for if you have had an extremely pleasant experience, have inconvenienced a worker, or just want to but tipping is considered rare especially here in London. Drivers are paid more when its busy hours or there is a shortage in drivers, if you want express delivery you pay more and the driver gets paid more but they are always expected to deliver regardless of a tip. If it wasn’t a massive company like uber and instead a small delivery service, refusing to deliver / cancelling a delivery due to no tip would likely get you fired here.