I work as a freelancer, employed by my partner's limited company and I take a salary of £24,500 and am not a shareholder. My client is requesting that I go abroad for up to three years and work in the Far East. I would be back in the UK for approximately 30 days a year. This would be on holiday and I would not be working during this time in the UK. My limited company will be charging me out at nearly triple the rate that it does in the UK. I expect to be rewarded for this and will expect a doubling - at least - of my salary while I am working abroad. Am I right in thinking that I will not have to pay any UK income tax on my salary as I would be working full-time abroad for 48/49 weeks of the year? If I don't have to pay any tax (as detailed above) and I increase my salary, could HMRC see this as some form of tax evasion?

The new rules of UK tax residency are not simple. They can be found in the HMRC document RDR3. From what you have written it sounds as though you may possibly be non-UK tax resident from when you go abroad. If so, you will not be liable to UK tax on your employment income from work performed abroad. See the HMRC RDR3 document. HMRC would not see it as a form of tax evasion - you are simply being remunerated at a higher rate due to the different conditions of your new employment.