It's not just the government selling off kit dirt cheap, the MOD has messed up major procurement projects for decades. The UK Phantom springs to mind, the heaviest, thirstiest, costliest, slowest Phantom at the time (Excluding the F-4G), also Nimrod AEW, TSR2, F-111K, SA80, Nimrod MR4, Chinook HC.3 etc Money wasted!
The Avionics for the Tornado were tested on Buccaneers, and the pilots suggested canceling the Tornado and just build new Buccs with the up dated Avionics! Most UK programs seem to go way over budget, probably caused by the need to Anglicize off the self programs such as the Phantom!
The Harrier did need replacing, it had a few flaws, lack of range, lack of Radar, lack of payload, and it was a bit of a potential SAM magnet with a very large IR signiature right at the wing joint! But I don't think the F-35 is the Aircraft to replace it, or the F-16/F-18/F-14/A-10/F-111 etc! In my opinion they should scrap the program, and do as Mr Turnip says and transfer the the technology to other airframes! I always liked the YF-32 over the YF-35! Boeing looked into adding a lot of the F-35 tech onto the F-18E/F!
For the UK, I'd suggest buying the Dassault Rafale, and up grade the carriers as cat-trap ones with the money saved!