[Tomvart]

Here was me thinking that 'design creep' was a MOD affliction! It seems from comments here that it's quite common across the marine engineering spectrum!
In my time at BAE systems (aero) I witnessed many examples of the MOD requirements managers tinkering with the system requirements and the 'Spec' post CDR, despite dire warnings from the engineering teams, these seemingly small changes only served to destabablise a system design that had sometimes taken years to design, agree and fund. Much of the issue being that complex designs of a 'system of systems' have so many interdependencies upon each other, that even small tweaks here and there have the potential to undermine other systems functionality.

It needs a strong will and fine negotions skills for the supplier to manage this, sadly it looks like Fergusons were dealt a dud hand and were forced into late design changes against both thier advice and will.

I recall a major design change on Nimrod which essentially undermined the whole aircraft design, it occurred after the design freeze just after the critical design review and involved the MOD specifying new engines, to give more thrust, better fuel efficiency and quieter operation. All for the right reasons but sadly implemented at the wrong time, which proved disasterous for the aerodynamic performance of the airframe.
The problem being in Nimrod was the that engines were located in the wing nacelles at the wing root (perfect for a MPA) and as these new BR710 engines were much longer than the originals, the wing area needed to be increased, which had the impact of radically altering the aerodynamic performance of the aircraft when in level flight, BAE's engineering solution to fix this was either break the fuselage aft of the wing and lengthen the distance between the wing and tail, or increase the size of the tail area, the latter solution would require significant aft fuselage strengthening, understandably - both suggested solutions involved unfunded expense and would be time consuming - coming so late in the engineering life cycle. More importantly, they were both unfunded in the contract price, so despite dire warnings from BAE and DERA aerodynamicist at both Farnborough and Warton, MOD went ahead with the engine change without the recommended attending fuselage/tail changes, the resultant aircraft performance in level flight during the flight testing stage was 'as expected' and the MOD subsequently stated that the Aerodynamic performance of the aircraft would be unacceptable in operational use (despite BAE designing a software solution called SAS/SID (stability augmentation system/stall identification device), this was essentially a software programme sat in between the stick and the control surfaces, to smooth level flight and help warn the pilot of an impending stall.
This condition was one of the main reasons stated by HMG of why the platform was cancelled in the notorious SDSR of 2010, the blame, as ever was put on BAE and all remaining MRA4 airframes were childishly destroyed on the apron of the factory where they were built, and the manufacturer was then paid to keep quiet - very simlar to the TSR debacle, which was a far more famous casualty of major design creep.
The cancellation of both programmes were a collosal waste of taxpayers money, because despite the spiralling costs - both aircraft would have delivered huge capability in defence to the UK. The solution to the government created capabilities gap was a trans Atlantic shopping spree to buy far inferior aircraft from the US. Criminal!