Coke will tell Londoners how happy they are this summer with outdoor 'happiness meters'

Coca-Cola plans to tell people in London how happy they are this summer with the launch of a "Happiness Meter" across 300 digital billboards in the capital city.

The "Happiness Meter" will measure Londoners' happiness levels based on the number of positive or negative mood words used on Twitter in the region, as well as mentions of Coca-Cola's #ChooseHappiness marketing hashtag.

Coke says it was to increase London's happiness level by giving away cans of the drink at major transport hubs and from Coke-branded taxis.

The brand also plans to surprise people having their lunch in parks and communal areas by gifting them free branded cool bags, packed with Coke products.

And it's giving away prizes to callers with a competition on London radio station Capital FM.

The activity all forms part of Coca-Cola's wider "Choose Happiness" marketing campaign, which launched in Great Britain in March. The launch of the campaign coincided with Coke moving to a "one brand strategy" across major European regions - moving from promoting each brand separately, to advertising the entire range as one. The idea is meant to highlight the benefits of its full portfolio, particularly its no and low-calorie drinks.

Here's a happy cabbie handing out a freebie from his Coke-branded car.

This is what the Coke cool bags will look like.

Happy Londoners off to tweet about how happy they are on receiving their free Cokes.