 A prototype ZX81 was demonstrated to BBC representatives in January 1981 , while Sinclair 's local rival Acorn Computers put forward their proposed Proton computer , a design – of which a prototype did not yet exist – based on the Acorn Atom . To Sinclair 's dismay , the contract to produce the BBC Microcomputer went to Acorn , which launched the machine in January 1982 . Paul <unk> , the producer of The Computer Programme , explained his reservations in a March 1982 interview with Your Computer : 
