If you ask ten people doing exactly the same tasks whether they are undertaking any "R&D", you will often get ten different answers, ranging from 0% to 100%!
A person's intuitive understanding of the boundaries of R&D tends to be affected by their background and experience - and often the more expert they are, the less they are inclined to think they are doing anything difficult. For a person whose whole life is making advances and solving technological uncertainty, it is easy to conclude that this is "Business as Usual" and not significant R&D.
So when the R&D tax relief regimes were first introduced the DTI (now BIS) drew up a definition of R&D for Tax Purposes - The Guidelines. These are definitive, but it takes care and experience to absorb the implications of all the sections therein. Generally people are put off by the first page, and it is probably true to say that more activities are eligible than people tend to think at first sight. Our experience is that at least a thirty minute discussion with a company's technologists is needed, so that they understand the critical distinction between eligible activity and routine "product development".
For those who like detail, the Guidelines are here: