Yes, you can use Holts Radweld before an MOT. A leaking radiator can be expensive to repair, and could cause your car to fail its MOT, so solving the problem at home first can be an ideal solution.
An MOT inspection is a thorough test of your vehicle’s roadworthiness, so if there are other problems with your vehicle, the MOT tester may still recommend additional work is carried out before it is passed. Using Radweld doesn’t guarantee your car will pass the MOT, but it will quickly and permanently repair leaks and help you to avoid costly radiator repairs.