Structuring a long contract in Saudi Arabia

Note: the original user wished for this question to be posted anonymously.

I am a computer contractor about to embark on an assignment which could be for 18 mths to 2 years in Saudi Arabia.

I have a UK LTD company but am advised I will still have to pay employers NI contributions on my income. An agency has been commissioned purely for payroll purposes by my clients. What is the most efficient way of structuring for this assignment? Is 'sole trader' an option or indeed 'employee of my client for the duration of the assignment'. Is setting up an offshore company an option?