Three London bus stops have been turned into Twitter vending machines for the next two weeks, until 10 September, ready to hand out free bags of Walkers crisps in return for Twitter postings.As part of the Do Yourself a Flavour competition, which invited consumers to suggest new flavours of crisps, the six finalists are available from the vending machines for the public to try. Visitors to the bus stops need to tweet @Walkers_busstop with a code provided to them after they arrive in order to bag a free, er, bag.Only 260 packets per bus stop will be available each day, so if you fancy heading down, you should do so earlier than later.The Walkers crisps brand is synonymous with BBC football\u00a0host and ex-England star Gary Lineker, and the flavours on offer are\u00a0Sizzling Steak Fajita, Chip Shop Chicken Curry, Pulled Pork in a Sticky BBQ Sauce, Ranch Raccoon, Cheesy Beans on Toast and Hot Dog with Tomato Ketchup. They are also available to buy in shops and customers are urged to vote for their favourite at walkers.co.uk.The winner will get a staggering \u00a31 million.Walkers' Twitter vending machines are hosted in bus stops in Oxford Street (two of them) and Clapham Junction."Walkers loves bringing fun to the nation and we are extremely excited to launch the UK\u2019s first ever tweet-powered vending machine on the streets of London," said the company's marketing manager Lee-Teng Chung."The Do Us A Flavour campaign has taken the nation by storm so we are delighted to offer the public the chance to try the new flavours in such an innovative way. We can\u2019t wait to hear more about what they think of the unique flavours."While this is the first Twitter-powered vending machine in the UK, Cadbury's unveiled a Facebook-powered vending machine\u00a0in Australia recently and Kelloggs created "Tweet Shop"\u00a0in central London in 2012, giving away free snacks for\u00a0Twitter postings.