Tossed have a range of branches in Central London, London shopping centres and at stop-off points on various motorways. Their food is well-labelled and includes vegan fare and gluten-free items. The former includes bagels, wraps, bowls and protein shakes. As items vary from one place to the next, check their website, but you can rest assured there are multiple options for vegans on the go.
(can vary during public holidays)