In the Javelin, "the Sapphire 204's afterburner could only be engaged at high altitude; due to the limited throughput of the fuel pump system; if reheat were engaged at low altitudes, it would actually cause a loss in thrust." - source;
http://www.vectorsite.net/avjavlin.html
The Javelin had a fairly limited reheat capability, yet, around the same period of time, Avons in the Lightning produced massive increases in thrust when reheat was engaged. What prevented the installation of a better reheat system on the Sapphire / Javelin? Was it a case that the airframe wouldn't benefit much from / couldn't cope with any further increase in thrust? Or perhaps that the increased fuel consumption of a better reheat system would have reduced the endurance by too much? Or something else?