When you say "subsidised the business" you mean paid necessary trading expenses for your sole trader enterprise out of money earned in Paye job?
A loss on the sole trader business can be used to offset taxes paid in Paye. In the "self-employed income" section of the Form 11 there is a section headed Losses, which asks if you wish to claim under S381 to offset losses of the trade against other income. Just put the amount of the loss in there.