Keys, wallet, mobile phone: it’s a mantra that many feverishly repeat each morning amid the rush to leave home. Yet for years, technology has held out the promise that one day, this will be reduced to just a phone.

The idea of one device carrying all the information needed to board a train, gain access to the office and buy a sandwich at lunchtime is enticing – but has so far failed to materialise in any widely available commercial form.