Tight rope indeed....
If yourcompany pay tax in Congo, it will not be offset against your UK tax. This can only happen if you pay tax to the Congolese authorities BUT there are two ways to offset it.

If you're based on land and working 28/28, then you are liable for full tax as you are still a resident of the UK.

The tax office at East Kilbride deals with the ofshore oil industry and can be helpful in answering any questions.

If you are not being paid by a UK company and therefore are not taxed at source, my advice would be to get an accountant to sort it for you.

Shanny