contracting abroad for UK agency

[Brussels Slumdog]

Which African country ?

Without knowing which African Country you are currently working it's difficult to give advice.
If you hold a "Resident Permit" then any efficient government will know that you exist which would make you a tax resident.
If you are working in say Somalia then I doubt that they would send you a tax return

[BlasterBates]

I would check on whether your taxable in Africa, you're not an employee of the UK government part of the embassy staff, so how are you registered? If the embassy has registered you as part of their staff I can see that you wouldn't be expected to pay tax, but since you are not a civil servant I wouldn't assume it's automatic, and I assume the embassy aren't necessarily going to protect a contractor. Anyway don't trust what your agency has said, they're not qualified to know.

The fact that you've maintained your residence and you return to it does mean HMRC might see you as resident. Anyway your accountant is probably best qualified to advise on that.