do I need planning to replace old concrete pads into one slab for my mobile home

Context is important with this question. Is the mobile home an annex to a house? or is the mobile home on its own land? Typically Permitted Development may cover this situation if the pad is below 300mm from finished ground level. The best solution would be to contact your local planning department or attend a surgery session most planning departments offer to clarify the situation. Hope that helps.

no you do not need planning permission of the pad is no higher than 300mm