BBC base their project on a microcomputer in their TV series The Computer Programme (1981). The list of topics included programming, graphics, sound and music, teletext, controlling external hardware, artificial intelligence, etc. The BBC decided to distinguish a microcomputer, then elaborated a fairly ambitious specification (for its time) and requested offers
The BBC discussed the problem with Sir Clive Sinclair, who tried to offer the failed microcomputer Grundy NewBrain, but was nowhere near the specification that the BBC had drawn up, and was rejected. The BBC arranged appointments to see other British computer manufacturers, including Dragon Data and Acorn computers.
The Acorn team had been working on improving their existing Atom microcomputer. Known as the proton, it included better graphics and a faster CPU 6502 of 2 Mhz (MOS Technology). At that time, the machine was only in prototype form, but the Acorn team, which depended largely on students at Cambridge University (such as the legendary Sophie Wilson and Steve Furber), worked all night long to have a proton Functional to show the BBC. The proton Acorn was not only the only machine that complied with the BBC specification, it also exceeded it in almost every field. He was a clear winner.
It is rumored that the BBC originally rejected the proton, alleging that it did not correctly represent the modern era of the computer. In response to this, the Acorn submitted the proton again, this time with the function keys painted in bright orange, without any other change. He was accepted.