It was 150 years from Leibniz to Boole and another 40 years to Frege. Each advance seemed obvious once it had been made, but apparently we earthmen are not very good at understanding our own conscious mental processes. An important scientific advance was made in the late 1970s and the 1980s. This was the formalization of nonmonotonic logical reasoning. Not mentioning it in discussing the last 20 years of AI is like not mentioning quarks in discussing the last 30 years of physics, perhaps on the grounds that one can build nuclear bombs and reactors in ignorance of quarks.
Logic needs further improvements to handle common sense properly, but no one knows what they are.
I don't suppose the Lighthill Report did much harm except to the British competitive position. Government officials today tend to ignore science in planning the pursuit of competitive technological advantage. It's hard to tell about ICOT, but they have been getting better recently. Some of the goals they set for themselves in 1980 to accomplish by 1992 require conceptual advances in AI that couldn't be scheduled with any amount of money. At present there is a limited but useful AI technology good enough for carefully selected applications, but many of the technological objectives people have set themselves even in the short range require further conceptual advances.