MD, I would think that a lot of us are asking the same question. Hopefully a few here will give you some good answers. I'll stick my head over the thingy and offer this.
The UK armed forces are still bloody good, but suffered repeated cuts since the end of the Cold War - actually since the end of WWII, but if you go back there we'll never get an answer. There has been a continuous disconnect between certain politicians (many of whom have little understanding of how the Armed Forces wok) and various parts of the MoD. At times, the disparate need to save money for other departments' use has led to delaying spending on projects, which does three things: it saves money this year, it delays the programme, it makes the programme more expensive.
As Defence spending has shrunk, so have the Defence industries. Therefore companies merge until the UK ends up with one main contractor that does everything. A virtual monopoly supported by the faith that the Government will always want to support the national economy and, therefore, always buy British or, at least, buy from a consortium or project that includes the remaining UK Defence industry. Therefore, the remaining main contractor holds all the trump cards.
UK Government is not willing to, or feels unable to, commit to a major programme alone in the belief that sharing risk, development costs and production costs will save them money. They overlook the consequences of multinational disagreement or failures by other nations contractors and the effects that these factors will have on the project's timeline and its costs.
The customer spends a lot of time deciding what its requirement may be. Then new people take over the job at MoD and decide that they didn't get it right and make changes. Industry tries to adapt the design to accommodate the changes, but this takes time, costs money and leads to other complications in the design, some of which will resurface later as issues later in the programme.
The next Government decides to make make defence cuts. So, priorities in existing programmes have to change. Changes to a programme leads to delays and cost. Something gets cancelled and another programme has to try to pick up the slack.
The country gets involved in an overseas conflict. Existing equipment doesn't conform to the operation. Let's say they don't have a certain piece of equipment that another, bigger country requires the UK's aircraft to have in order to join in the fight. The MoD has to drop everything, find emergency funding and a way to buy and incorporate the required equipment in their aircraft. Well, some of them. After the conflict is over, the MoD has a number of aircraft at a different standard to the rest. Now what? You know the kit is needed in the whole fleet, but where does the money come from?
And on and on and on. Everyone wants a world-beating Air Force. No one wants to fund it properly. Kit gets more and more expensive. Kit wears out and must be replaced. Politicians believe that saying they love the Forces will make it OK. No will to spend money in peacetime, a desperate wish to deploy forces when it gives the polis a place on the world stage.
Some countries have the guts to go ahead and do it alone. Well almost. The U.S. do it, but have recently been bitten by costs and delays in some recent programmes. But they keep doing it and they are very big. France does it because they're like that. Sweden do it. So maybe it's something to do with government determination.
In short, mopardavd, I have no idea.