Ministers have been urged to intervene after it emerged that more than a third of vouchers intended to ease the energy bills of people on prepayment meters have not been redeemed. Data released on Tuesday by the Department for Business, Energy and Industrial Strategy showed that 34% of vouchers have not been redeemed since the scheme launched in October. The energy bills support scheme was introduced to soften the blow of rising bills this winter. The energy price guarantee cuts bills for people on direct debits while the voucher scheme was designed to help those on prepayment meters. However, more than 1.3m vouchers remain unredeemed with many either lost, delayed or unclaimed. The Guardian revealed at the start of December that up to half a million of the UK’s most vulnerable families have been left without government help since October. In total, fewer than 2.7m of the more than 4m time-limited vouchers for £66 sent to households with traditional prepayment meters have been claimed. Consumer champion Martin Lewis joined with Which?, Age UK, Citizens Advice and National Energy Action to write to business secretary Grant Shapps expressing concern over the low redemption rate. “It cannot be right that millions of pounds of government support is going unclaimed while low income and vulnerable groups are at risk,” they wrote, in an open letter published on Tuesday. They called for the government to regularly publish redemption rates including the delivery method; investigate why redemption rates are low; raise awareness of the scheme and consider adapting it when issues are identified. “We understand that this is a new, complex scheme that has been implemented quickly during a challenging time. Nevertheless, we believe it is your responsibility, alongside government, to do everything you can to ensure this vital support reaches people as soon as possible,” they wrote. Earlier on Tuesday, Shapps accused some energy suppliers of not picking up the phone to customers. “What concerns me is that gap between vouchers being sent out and people finding the voucher,” he told ITV’s Good Morning Britain. Dhara Vyas, deputy chief executive of industry body Energy UK, said: “Suppliers are doing everything possible to ensure that the vouchers are reaching customers and will make repeated attempts using the channels – such as text, email, phone or post – and contact details available to them.” The concerns over vouchers came amid calls from MPs for a ban on forced installations of prepayment meters amid fears that elderly and vulnerable people are being effectively cut off from heating and power supplies. Prepayment meters are being scrutinised as thousands of warrants allowing forced installations are being issued. On Monday, the government extended the existing support to allow people living in care homes and on caravan parks to receive £400 to help with their fuel bills. About 900,000 households in England, Scotland and Wales without a direct relationship to an energy supplier would be able to apply online for the £400.