Original computer programmes are protected as literary works under the Copyright Designs and Patents Act 1988 as amended by the Copyright (Computer Programs) Regulations 1992. This protects the source code written by the programmer, the program itself and the preparatory design material. What you see on the screen is protected separately by artistic copyright.
Nova Productions sued Mazooma Games over a game of computer pool. Mazooma admitted that its game had been inspired by Nova’s, but Nova claimed infringement of its copyright in its program. The Court of Appeal found for Mazooma.
In order for infringement to occur, there must be copying of a substantial part of the copyright work. The court found that there had been no copying of Nova's work, either in the source code or the screenshots. The court confirmed that "merely making a program which will emulate another but which in no way involves [substantially] copying the program code or any of the program's graphics is legitimate".
The case highlights the relatively limited protection available in copyright law for computer programs; only the graphics and source code will attract protection, and in order to establish infringement substantial copying must be proven.