There is a surprising dearth of experts in this thread, and I am not about to offer myself as one. However, a builder puchased a house opposite us, a Victorian terrace, in order to renovate it and sell it on. He was choked to discover it had dry rot that had spread up behind the plaster from the ground to the first floor. It did not have a basement. I saw some of the work he di to rectify it, and it consisted mainly of hacking off all the plaster and drilling a hole (or possibly two?) into each and every brick, and injecting some fluid into the holes. I presume woodwork was also replaced. I have no idea whether all that was essential, but I do know that everything he did was eating into his profit, so I assume it was essential.
Could you get Rentokill or some such outfit to give you a 'free survey' and quote? Perhaps your mortgage company would give an additional loan for such work - as it is protecting 'their' asset. It might be worth asking the council if they can offer any advise - or even a grant.
Have you done a google group search?
I have couple of url's you may not have seen;...
DRY ROT DEVELOPING A LESS DISRUPTIVE APPROACH TO DIAGNOSIS AND TREATMENT (Presentation to Glasgow West Conservation Trust Masterclass Series)
See also McGill's home page
A somewhat less erudite page