Threshold for repaying pre-1998 loans and self employment

Hi folks,

Hoping someone can give me an answer here - I've been trying to find out how gross income is regarded in respect to self employment. I've currently deferred my pre-1998 loans, but will be going self employed shortly, driving a black cab. My turnover will be above the threshold for repayments (around £39k), but I need to rent a cab, and obviously pay fuel etc. These costs will push me below the threshold (around £26k). I dont expect to be taxed on £39k, but will on the £26k.

Does anyone know which figure they will use when it comes to deferment? They ask for a gross figure before tax, and if this means £39k, the subsequently triggered loan repayments would probably prohibit me from going self employed.

For various reasons, I'm reluctant to ask the loan management company at this stage, so I'm hoping I can get an idea of how it works here?

Thanks for reading.