Brought to you by the same military that pissed 4 Billion up the wall with the nimrod debacle..
To be fair, the Nimrod was in comparison to any of it's competitors (including the P8, which we are going to replace it with) a spectacular aircraft in terms of performance so it was quite reasonable for the RAF to want to keep it with a few improvements, especially if the quote was competitive for doing so. BAE screwed up the project massively, not the RAF.
The problem BAE had was basically modern assumptions and working practices versus the assumptions and working practices of the 1960's.
Modern working practices are that design is done in CAD, and the parts are produced with computer driven equipment to ensure that every two parts are completely, perfectly identical with literally inhuman precision. In the 1960's when the Nimrod was made somebody actually hand made these parts on a Lathe to a paper plan with a human degree of precision.
Back in the 1960's, If a part was a tiny faction of an inch off when it came to fit it then the designers working with a slide rule and a pencil knew that'd happen when they designed it, the fitters knew it'd happen sometimes when they fitted the part, and the fitter reached for a file and filed it down so it'd fit (or it went back on a lathe to trim a thousandths of an inch off) and nobody thought anything of it because it was accepted practice with a small scale production run and fixing little issues like that was part of the job.
In the modern day and age, when the chap tries to slot the parts together and they don't fit everybody involved has a meltdown. The issue gets passed to the line manager, who immediately halts work and passes the issue up to his manager, and so on until it hits the project manager. A cloud of recriminations then drops downwards. Eventually somebody suggests filing a bit off to fit, to somebody sucking air in through their teeth and wondering about the design risk of doing so. A full engineering and risk management review is then conducted, which comes to the conclusion that as long as the two parts meet correctly then it''s as much of an issue as it has been since the aircraft entered service in 1970.
The part is duly filed to fit, and things proceed for another twenty minutes until the next time that 21st century manufacturing practices meet 19th century craftsmanship practices that persisted into the middle of the 20th century.
Rinse and repeat until a handful of the aircraft have been delivered, but the project has overrun for a decade. What somebody ought to have done was come to the conclusion early on that you couldn't interface the new computer built parts with the handmade parts and just built the entire thing from new parts.
This isin't a new issue even in the 20th century, look at the production of the Bofors gun. The Sweedes handbuilt 18 of them for what they wanted, built another 10 for export before then getting orders for a few hundred. These were built with instructions labelled "file this part to fit" before British and the later American mass production started on a larger scale with improved drawings (building a few thousand) and then epic scale when the Americans built an entire industry (~2000 subcontracters) around knocking them out in the tens of thousands with a high degree of precision.