So in 6 years the project is £2.35 billion overbudget of which just £74 million can be attributed to the Dave B / Dave C debacle.
What we have here is more rehashing of old news to make it seem the thing is still going disastrously wrong. The original MG in 2007 had a price of £3.9Bn, which lasted as long as the various reprofilings in 2008, which completely screwed the budget (by over £1Bn). In fact, as long ago as the 2010 MPR, the forecast outturn cost was reported as being £5.9Bn.
What I suspect this is, is BAES striking a price for surrendering a fairly strong contractual position, which (if you believe the PAC & NAO) basically means they make a profit unless the ship cost exceeds £7.5 Bn or some such ludicrous number. In other words, they could "legitimately" charge staff costs only loosely attributable to the carrier project to it, right up until they hit that penalty barrier, while still making a profit (allegedly).
Who is responsible for that situation (if it indeed exists) is a different question. It does however highlight that MoD commercial and cost estimating capabilities remain less than optimal, as does the sole-source by default arrangment that they have allowed (indeed encouraged) to develop.
Its a shame the media feels the need to use phrases like "costs to double" implying this is a recent event, rather than accurately report that closing off contract risks has cost another £300M. However, that's what you get when a government spends several years vacillating, places an order, then changes the delivery date, before another one comes along once the project is running and tries to change a contract before changing its mind again.