I’ve been playing around a bit more with the English Heritage Excavation Index (see previous). The majority of the records in the Index have been given a start and an end date for the investigation undertaken, with the first one happening in the 13th century! We can take these start / end dates and divide by time slices and then collate by hexagonal bin to create an animation of archaeological investigation in England over the last few hundred years (you may need to click on the image to see the animation):
Although this is unlikely to be a perfectly complete picture, it is quite an interesting one, I think. Some of the persistent areas of investigation in the 19th century are likely to be due to uncertainly recorded start / end dates rather than work that lasted for decades, but this factor should be minimal from 1900 onwards.