rent out on residential mortgage

i bought a flat in april but due to unforeseen circumstances i need to move back in with my parents (health issues). so now i want to rent the flat to a friend but can she just send me rent money or will my mortgage provider not allow this? and how would they find out? i'm thinking i should just contact my mortgage provider and ask if i can get a consent to let but im worried my interest rate might increase.

any thoughts?