The first ones have been build in Japan and my understanding is that the rest from next year are being assembled in the UK.
All things these days are done on price / performance / reliability / delivery timescales / in-life running costs basis. This is not a combination that the UK has any reputation for fulfilling compared to countries like Japan and Germany. In fact we have a long history of failure on these terms.
Although UK lead the industrial revolution, the reality is that we have not been competitive since the 1890's in most areas of engineering and production. This is due to a combination of our class structure, poor politicians, management, infrastructure, investment, training, access to finance and trade union demarcation lines and bloody mindedness.
At the end of WWII the Atlee Government spent our Marshall plan money (which was more than Germany's and Japan's) on nationalization and setting up the welfare state. Germany and Japan invested in their industries and used the generated wealth from profits to tax and then create their welfare states. Who were smart and who were the fools?
In Germany much of their industry is funded by local investment by local family banks into local family owned companies. This means that SME's have much easier access to local finance as lower cost than we do in the UK.
Big projects require access to many local different products and these local engineering and production companies, just no longer exist in the UK. In Germany, Japan, Korea, Taiwan and China, what you need can generally be locally sourced.
The UK is now classed as a post industrial service based country. Fortunately, we are rather good at international law, finance, insurance and software development all of which make a positive contribution to our poor balance of payments. Experience shows that it takes about 100 years to build an international legal / financial centre like London, China has been very lucky to inherit one with Hong Kong.