Good article on the P.1154 from which I've lifted the following -
"...a Labour government came to office dedicated to making economies in defence expenditure......RAF was dedicated to preserving the TSR 2, as it was seen to provide the core capability that justified the Service's full independence...The RAF decided not to oppose the cancellation of the P.1154 too vigorously and to gamble all on the TSR 2."
&
"Although the TSR 2 was a triumph of 1950's technology, its prospects of being exported looked extremely poor due to its high costs and complexity. On the other hand, the P.1154 represented the last all-British entry in the key supersonic fighter market that has provided the bulk of exports for combat aircraft in the 1970's, 80's and 90's. At the time of its cancellation many countries were still pursuing the goal of survivable, effective airpower that aircraft such as the P.1154 offered. While the subsonic Harrier has proved modestly successful in the export field, the availability of the more capable P.1154 could have strengthened the customer base for V/STOL combat aircraft, providing a much greater success in the one area of aviation where Britain had genuinely led the world."
Worth a read
The P.1154 story