You shouldn’t take out any loans or other forms of credit while in a Trust Deed, or other formal debt solutions like the Debt Arrangement Scheme.
If you do apply for a loan while in a Trust Deed and you are successful in your application, you will still be liable for the debt and can’t add it to the Protected Trust Deed at a later date.
However, it is possible that you can apply for finance on a car as they are generally classed as an essential expense. If you do intend to apply for Car Finance whilst in a formal debt solution such as a Trust Deed then the Trustee must approve the request first.
You will also need to demonstrate that the repayments of the Car Finance are affordable for you too.