To obtain a Sole Representative Visa, you do not have to be employed by the company for any specific duration of time. You do need to however prove that there is a clear employee-employer relationship between you and the company and that you have experience and expertise in your field of work. This can be from previous projects or jobs. If the sole purpose of your employment is to send you to the UK as the sole representative, it is also advisable to submit the interview notes to demonstrate why you have been appointed for this position. Your appointment should have been for your skills. The main aim of this is to make sure that you have an appropriate level of seniority to make decisions on behalf of the overseas business whilst in the UK and that your post was not created for the purpose of you getting a sole representative visa.