Is there anywhere that 'officially' states text height, layer names etc.... I know text height is 2.5 and have used that for years, I'm in a new job and their cad technician has used height 2mm for a few years and i'm trying to set a professional standard within the company as asked. 

It depends on what field you are working in (ex. - architectural vs. mechanical) and what standards, if any, the company you work for has already established.I see you are in the U.K.  Re: standards.  Have you ever heard of BS 8888?  That would be the British standards for technical products specification.