National Grid, Britain's biggest distributor of gas and electricity, has attacked the energy regulator Ofgem's plans for the upgrade of the UK's power networkThe FTSE 100 firm says the initial plans, which envisage up to £22bn of investment between 2013 and 2021, "differ substantially" from its own business plan.National Grid goes on to say the plan: "will not appropriately incentivise the essential investments necessary to provide safe, reliable networks for the UK consumer..."The company says it will challenge Ofgem over the financing packages that have so far been outlined.In its own statement today, Ofgem concedes that its package of proposals will see household bills rise by an average of £7 in 2013, rising to £15 by 2021. It is likely National Grid will argue those increases will not be enough.Just after the open National Grid shares had dropped 2.2%BS