 After viewing the completed 25 @-@ minute pilot , " <unk> in the Sky " , Lew Grade was so impressed by APF 's work that he instructed Anderson to double the episode length and increased the series ' budget per episode from £ 25 @,@ 000 to £ 38 @,@ 000 . As a result , Thunderbirds became not only the company 's longest and highest @-@ budgeted production , but also among the most expensive TV series to have been made up to that point . The crew , who had been filming at a rate of two 25 @-@ minute episodes per fortnight , faced significant challenges during the transition to the new format : eight episodes had already been completed , scripts for up to ten more had been written , and substantial <unk> would be necessary to satisfy the longer running time . Anderson lamented : " Our time @-@ scale was far too drawn out . ITC 's New York office insisted that they should have one show a fortnight ... Everything had to move at twice the speed . " APF spent over seven months extending the existing episodes . 
