0898andy

I have an old outdoor patio with tiles laid on mortar beds on top of a 6 inch concrete pad. I want to replace the old concrete tiles with vitrified porcelain tiles I've purchased. Can I remove the old tiles and tidy the concrete dabs/pads down to the original concrete pad and lay the porcelain onto the concrete pad ? or do I need to removed the concrete pad and lay new substrate ? The pad is sound and solid it just has marks from the old dabs of mortar from the original tiles. This is the North UK.