Will I have to provide a personal guarantee if I take out a Ltd Co buy to let mortgage?

Yes. All lenders will require that the directors/majority shareholders provide personal guarantees.

Related questions:

Are limited company buy to let mortgages harder to get?

Are limited company buy to let mortgages more expensive?

Will I have to put in a bigger deposit if I borrow through a limited company?

Is there a particular type of limited company I should establish in order to purchase buy to let properties?