http://www.youtube.com/watch?v=WeerxAO3oRU Here is a marshall factory tour from last year. They are using auto insertion machines, wave solder machines, various lines etc. Also sounds like they are doing their own wood and metal work. Doing their own QC. The PCB's are made over seas but not populated, not sure about their transformers these days... but unless they've changed vastly in the last year, I'd call that British Made. I just went through the process of drawing up a power supply PCB for a valve amp and sending it to China for prototyping and the cost was much less than trying to do the same job within the UK (which is a bit sad to be honest). I think once a company has a certain level of demand for products then they have to shape their construction methods to fit if they want to keep up with that demand. Otherwise you put up prices to suit demand and operate in a boutique sense I guess.
As for the point about the hand wired series. Those amps represent products and build techniques from the lates 60's. 15 years ago Marshall was releasing the JCM2000's which is a range of amps I don't like from a sound and construction point of view. I also think, that for totally hand wired amps the cost to the consumer is probably quite competitive compared to other British companies making similar hand wired turret based amplifiers. There is no point in Marshall trying to sell those amps at the same cost as the machine constructed amps as selling them at that price would probably be making them an overall loss.
Valvestates aren't really hiding the fact they are hybrids. They have 'state' in their name. I prefer them to the AVT range. The JCM900 4100 sounds cruddy and that has a hybrid preamp with valve power amp. What if the guys at blackstar developed the valvestate, AVT, JCM900 ranges for marshall? What if the Blackstar amps are just an extension of that work were they actually got a good tone nailed down? Could be the case. As far as SS goes. I don't have a problem with it but I think it has some advantages and possible applications in which it rarely seems to be used. Blackstar doesn't say their amplifiers are based on the same technology has JCM high gain dual reverbs, but when you see what features they offer, compared to the valve compliment, it makes sense that they have a bit more than a solid state loop in them.