Warning lights after doing engine work

[Tess P]

Hi, quick Q. I've just replaced the timing belt/water pump and gasket with my dad. The car is driving great. But two warning lights appeared - the engine warning and electronic stability control lights as soon as we started the engine after doing the work. Is this simply because we've been doing work on the car? And if so, how do we get rid of them prior to MOT? As I said, it's driving fine at 80mph, just did London-Manchester with no issues, no noises, no smells. Thanks in advance.