By Jessica Frank-Keyes Rail renationalisation will save the taxpayer £2.2bn every year, Labour’s shadow transport secretary has claimed, thanks to “significant efficiencies”. Louise Haigh promised Labour’s plans to bring Britain’s railways back into public ownership would “save the taxpayer billions of pounds every year” and contribute to all five of her party’s missions for government, on: growth, energy, health, safety and opportunity. She told journalists at Trainline HQ in central London this morning: “Obviously, we are in a very constrained public spending environment. There is no doubt a…