Perhaps. If you accept that there is no valuation method (in the same way that it is difficult to value someone's life), then a way around this is to use an 'auction' method of valuation; where people are asked to put a value on what it is worth to them.

One method of doing that is called the "Contingent Valuation Assessment"[CVA]. In the absence of any proof that something has any definable value, this can be used to get a perceived value that can be assessed against options to do (or not do) something. This is the method that has been used by Highways. It tends to overestimate value but can also underestimate it.

Because either a) archaeology is impossible to value or b) insufficient work has been done to value it properly, the method used has been "CVA". It's just an opinion Nigel, but arguing that it's impossible to value archaeology probably won't help the case of the 21 archaeologists (in essence the case that they would need to develop is that archaeology is more valuable than Highways have estimated). From what I can see, the CVA method used would be independently assessed as having been very generous to the archaeology.