The Chinook was originally bought from the Yanks for the RAF in the '60s. Because this helicopter was bought off-the-shelf and worked perfectly well, BAe Systems were brought in to try and fuck it up - and truly excelled themselves. The result was the Chinook HC3 (Helicopter, Cake & Arse Mark three), desgined to deliver THEM behind enemy lines, in all weathers. Unfortunately, the software could not be certified to UK standards, so they were limited to daytime, good weather flying. Eventually, a compromise was reached at which the taxpayer would pay a further vast amount of money, and the problems would be fixed.
Of course, this was then cancelled - and the Chinooks were reverted back to HC2 (the same as the rest of the fleet) standard. For a further £50 or £60 million. The current estimate of the whole programme cost is £500 million for 8 aircraft - the unit cost of a normal Chinook is estimated at $35 million at 2008 prices (less than £25 million) - so each helicopter cost about two and a half times as much as it should.