Are BMA calculations that resident doctors need a 29% pay rise credible?

The union bases its claims of a real-terms cut on the retail prices index – ditched as a national statistic in 2013

The British Medical Association (BMA) is demanding a 29% pay rise for resident doctors, formerly known as junior doctors, in England, to prevent strikes. The union claims the increase is needed to reverse cuts to the real-terms value of their pay since 2008. But how credible are its calculations?