How much will Truss's energy plan cost?

<div>Today Liz Truss has announced in parliament an energy price cap to tackle rising bills. As of October, the average household energy bill will be frozen at £2,500 for the next two years. How effective will this be? And how have her free market allies reacted to her use of price controls? <br> <br> James Forsyth and Katy Balls discuss. </div>