Controlled Temperature Coefficient of chip resistor
One problem with your circuit is that it is sensitive to transistor hFE. The feedback current is related to Ie of T2 but you care about Ic. T1 may start to compound the issue at higher currents and/or higher ambients by diverting base current from T2. As the temperature of T1 increases the hFE also increases, so the collector current will drop. 

Ignoring the function of T1 for now (which I assume is to limit the output current even under fault conditions),  consider replacing T2 with a MOSFET suitable for the power dissipation requirements (at 12V a TO-92 such as 2N7000 may be okay). A darlington pair with two NPN would also be an improvement but at a cost in voltage drop. 

Consider adding a 2nd op-amp as a clamp on the non-inverting input of U1 rather than R6/T1. So a diode, op-amp and 2 resistors to create a reference. You will gain a bit of compliance voltage by eliminating R6 so more than 0.4V. You could spend that by increasing R5 to 49.9 ohms which makes the circuit less sensitive to the offset and TCVos of that rather low-end op-amp.