ruction ▁of ▁the ▁first ▁SR . 5 3 ▁prototype ▁took ▁longer ▁than ▁anticip ated , ▁in ▁part ▁due ▁to ▁de ▁Hav ill and ▁having ▁problems ▁deliver ing ▁the ▁Spect re ▁engine ▁on ▁time , ▁installing ▁auxili ary ▁equipment ▁was ▁also ▁time - consum ing . ▁According ly , ▁the ▁ma iden ▁flight ▁of ▁the ▁SR . 5 3 ▁began ▁to ▁fall ▁further ▁and ▁further ▁behind ▁schedule . ▁ ▁The ▁date ▁of ▁the ▁first ▁flight ▁was ▁first ▁set ▁back ▁to ▁March ▁ 1 9 5 5 , ▁and ▁then ▁into ▁ 1 9 5 7 . ▁Un ique ▁challeng es ▁were ▁pos ed ▁by ▁the ▁HT P ▁fuel , ▁including ▁the ▁development ▁of ▁suitable ▁storage ▁b ags ▁and ▁the ▁fuel ▁flow ▁proportion er . ▁In ▁January ▁ 1 9 5 4 , ▁the ▁Ministry ▁reduced ▁its ▁order ▁from ▁three ▁SR . 5 3 ▁pro tot ypes ▁to ▁two , ▁which ▁were ▁constructed ▁side ▁by ▁side ▁at ▁Sau nd ers - R oe ' s ▁Cow es ▁facility . ▁Development ▁with ▁the ▁compet ing ▁Av ro ▁ 7 2 0 ▁proceeded ▁more ▁smooth ly ; ▁by ▁ 1 9 5 6 , ▁its ▁prototype ▁was ▁virt ually ▁complete ▁and ▁was ▁viewed ▁as ▁being ▁capable ▁of ▁flying ▁up ▁to ▁a ▁year ▁ahead ▁of ▁the ▁lag ging ▁SR . 5 3 . ▁ ▁By ▁September ▁ 1 9 5 3 , ▁the ▁programme ▁to ▁develop ▁these ▁aircraft ▁came ▁under ▁scr ut iny ▁due ▁to ▁a ▁need ▁to ▁implement ▁cost ▁cut s ; ▁as ▁a ▁result , ▁the