Hi, It depends on the MOT Station, they are now very very strict on any additions & items that should not be there RE/ your Lap belt, They will know that the car came with as you replied & to me I do not think they will they will jeopardize their Licence for the sake of a belt also to add, just think ahead on this I hope for you it never does but if an accident occurs with your car and there is someone hurt someones Insurance will be on to this in an instant, my advise would be get a replacement from a scrap yard the cost will be in the region of �!0/ �15, It will be worth it! do you not think?